diff --git a/src/primaite/common/enums.py b/src/primaite/common/enums.py
index db5d153c..ff090ca9 100644
--- a/src/primaite/common/enums.py
+++ b/src/primaite/common/enums.py
@@ -148,6 +148,7 @@ class ActionType(Enum):
     ANY = 2
 
 
+# TODO: this is not used anymore, write a ticket to delete it.
 class ObservationType(Enum):
     """Observation type enumeration."""
 
diff --git a/src/primaite/environment/primaite_env.py b/src/primaite/environment/primaite_env.py
index 5bf843f1..d1c8adf5 100644
--- a/src/primaite/environment/primaite_env.py
+++ b/src/primaite/environment/primaite_env.py
@@ -562,7 +562,7 @@ class Primaite(Env):
         else:
             return
 
-    def apply_actions_to_acl(self, _action):
+    def apply_actions_to_acl(self, _action: int) -> None:
         """
         Applies agent actions to the Access Control List [TO DO].
 
@@ -640,7 +640,7 @@ class Primaite(Env):
             else:
                 return
 
-    def apply_time_based_updates(self):
+    def apply_time_based_updates(self) -> None:
         """
         Updates anything that needs to count down and then change state.
 
@@ -696,12 +696,12 @@ class Primaite(Env):
 
         return self.obs_handler.space, self.obs_handler.current_observation
 
-    def update_environent_obs(self):
+    def update_environent_obs(self) -> None:
         """Updates the observation space based on the node and link status."""
         self.obs_handler.update_obs()
         self.env_obs = self.obs_handler.current_observation
 
-    def load_lay_down_config(self):
+    def load_lay_down_config(self) -> None:
         """Loads config data in order to build the environment configuration."""
         for item in self.lay_down_config:
             if item["item_type"] == "NODE":
@@ -739,7 +739,7 @@ class Primaite(Env):
         _LOGGER.info("Environment configuration loaded")
         print("Environment configuration loaded")
 
-    def create_node(self, item):
+    def create_node(self, item: Dict) -> None:
         """
         Creates a node from config data.
 
@@ -820,7 +820,7 @@ class Primaite(Env):
         # Add node to network (reference)
         self.network_reference.add_nodes_from([node_ref])
 
-    def create_link(self, item: Dict):
+    def create_link(self, item: Dict) -> None:
         """
         Creates a link from config data.
 
@@ -864,7 +864,7 @@ class Primaite(Env):
             self.services_list,
         )
 
-    def create_green_ier(self, item):
+    def create_green_ier(self, item: Dict) -> None:
         """
         Creates a green IER from config data.
 
@@ -905,7 +905,7 @@ class Primaite(Env):
             ier_mission_criticality,
         )
 
-    def create_red_ier(self, item):
+    def create_red_ier(self, item: Dict) -> None:
         """
         Creates a red IER from config data.
 
@@ -935,7 +935,7 @@ class Primaite(Env):
             ier_mission_criticality,
         )
 
-    def create_green_pol(self, item):
+    def create_green_pol(self, item: Dict) -> None:
         """
         Creates a green PoL object from config data.
 
@@ -969,7 +969,7 @@ class Primaite(Env):
             pol_state,
         )
 
-    def create_red_pol(self, item):
+    def create_red_pol(self, item: Dict) -> None:
         """
         Creates a red PoL object from config data.
 
@@ -1010,7 +1010,7 @@ class Primaite(Env):
             pol_source_node_service_state,
         )
 
-    def create_acl_rule(self, item):
+    def create_acl_rule(self, item: Dict) -> None:
         """
         Creates an ACL rule from config data.
 
@@ -1031,7 +1031,8 @@ class Primaite(Env):
             acl_rule_port,
         )
 
-    def create_services_list(self, services):
+    # TODO: confirm typehint using runtime
+    def create_services_list(self, services: Dict) -> None:
         """
         Creates a list of services (enum) from config data.
 
@@ -1047,7 +1048,7 @@ class Primaite(Env):
         # Set the number of services
         self.num_services = len(self.services_list)
 
-    def create_ports_list(self, ports):
+    def create_ports_list(self, ports: Dict) -> None:
         """
         Creates a list of ports from config data.
 
@@ -1063,7 +1064,8 @@ class Primaite(Env):
         # Set the number of ports
         self.num_ports = len(self.ports_list)
 
-    def get_observation_info(self, observation_info):
+    # TODO: this is not used anymore, write a ticket to delete it
+    def get_observation_info(self, observation_info: Dict) -> None:
         """
         Extracts observation_info.
 
@@ -1072,7 +1074,8 @@ class Primaite(Env):
         """
         self.observation_type = ObservationType[observation_info["type"]]
 
-    def get_action_info(self, action_info):
+    # TODO: this is not used anymore, write a ticket to delete it.
+    def get_action_info(self, action_info: Dict) -> None:
         """
         Extracts action_info.
 
@@ -1081,7 +1084,7 @@ class Primaite(Env):
         """
         self.action_type = ActionType[action_info["type"]]
 
-    def save_obs_config(self, obs_config: dict):
+    def save_obs_config(self, obs_config: dict) -> None:
         """
         Cache the config for the observation space.
 
@@ -1094,7 +1097,7 @@ class Primaite(Env):
         """
         self.obs_config = obs_config
 
-    def reset_environment(self):
+    def reset_environment(self) -> None:
         """
         Resets environment.
 
@@ -1119,7 +1122,7 @@ class Primaite(Env):
         for ier_key, ier_value in self.red_iers.items():
             ier_value.set_is_running(False)
 
-    def reset_node(self, item):
+    def reset_node(self, item: Dict) -> None:
         """
         Resets the statuses of a node.
 
@@ -1167,7 +1170,7 @@ class Primaite(Env):
             # Bad formatting
             pass
 
-    def create_node_action_dict(self):
+    def create_node_action_dict(self) -> Dict[int, List[int]]:
         """
         Creates a dictionary mapping each possible discrete action to more readable multidiscrete action.
 
@@ -1202,7 +1205,7 @@ class Primaite(Env):
 
         return actions
 
-    def create_acl_action_dict(self):
+    def create_acl_action_dict(self) -> Dict[int, List[int]]:
         """Creates a dictionary mapping each possible discrete action to more readable multidiscrete action."""
         # reserve 0 action to be a nothing action
         actions = {0: [0, 0, 0, 0, 0, 0]}
@@ -1232,7 +1235,7 @@ class Primaite(Env):
 
         return actions
 
-    def create_node_and_acl_action_dict(self):
+    def create_node_and_acl_action_dict(self) -> Dict[int, List[int]]:
         """
         Create a dictionary mapping each possible discrete action to a more readable mutlidiscrete action.
 
@@ -1249,7 +1252,7 @@ class Primaite(Env):
         combined_action_dict = {**acl_action_dict, **new_node_action_dict}
         return combined_action_dict
 
-    def _create_random_red_agent(self):
+    def _create_random_red_agent(self) -> None:
         """Decide on random red agent for the episode to be called in env.reset()."""
         # Reset the current red iers and red node pol
         self.red_iers = {}
diff --git a/src/primaite/environment/reward.py b/src/primaite/environment/reward.py
index 9cbb0078..c9acd921 100644
--- a/src/primaite/environment/reward.py
+++ b/src/primaite/environment/reward.py
@@ -1,25 +1,32 @@
 # Crown Copyright (C) Dstl 2022. DEFCON 703. Shared in confidence.
 """Implements reward function."""
-from typing import Dict
+from typing import Dict, TYPE_CHECKING
 
 from primaite import getLogger
+from primaite.common.custom_typing import NodeUnion
 from primaite.common.enums import FileSystemState, HardwareState, SoftwareState
 from primaite.common.service import Service
 from primaite.nodes.active_node import ActiveNode
 from primaite.nodes.service_node import ServiceNode
 
-_LOGGER = getLogger(__name__)
+if TYPE_CHECKING:
+    from logging import Logger
+
+    from primaite.config.training_config import TrainingConfig
+    from primaite.pol.ier import IER
+
+_LOGGER: "Logger" = getLogger(__name__)
 
 
 def calculate_reward_function(
-    initial_nodes,
-    final_nodes,
-    reference_nodes,
-    green_iers,
-    green_iers_reference,
-    red_iers,
-    step_count,
-    config_values,
+    initial_nodes: Dict[str, NodeUnion],
+    final_nodes: Dict[str, NodeUnion],
+    reference_nodes: Dict[str, NodeUnion],
+    green_iers: Dict[str, "IER"],
+    green_iers_reference: Dict[str, "IER"],
+    red_iers: Dict[str, "IER"],
+    step_count: int,
+    config_values: "TrainingConfig",
 ) -> float:
     """
     Compares the states of the initial and final nodes/links to get a reward.
@@ -93,7 +100,9 @@ def calculate_reward_function(
     return reward_value
 
 
-def score_node_operating_state(final_node, initial_node, reference_node, config_values) -> float:
+def score_node_operating_state(
+    final_node: NodeUnion, initial_node: NodeUnion, reference_node: NodeUnion, config_values: "TrainingConfig"
+) -> float:
     """
     Calculates score relating to the hardware state of a node.
 
@@ -142,7 +151,9 @@ def score_node_operating_state(final_node, initial_node, reference_node, config_
     return score
 
 
-def score_node_os_state(final_node, initial_node, reference_node, config_values) -> float:
+def score_node_os_state(
+    final_node: NodeUnion, initial_node: NodeUnion, reference_node: NodeUnion, config_values: "TrainingConfig"
+) -> float:
     """
     Calculates score relating to the Software State of a node.
 
@@ -193,7 +204,9 @@ def score_node_os_state(final_node, initial_node, reference_node, config_values)
     return score
 
 
-def score_node_service_state(final_node, initial_node, reference_node, config_values) -> float:
+def score_node_service_state(
+    final_node: NodeUnion, initial_node: NodeUnion, reference_node: NodeUnion, config_values: "TrainingConfig"
+) -> float:
     """
     Calculates score relating to the service state(s) of a node.
 
@@ -265,7 +278,9 @@ def score_node_service_state(final_node, initial_node, reference_node, config_va
     return score
 
 
-def score_node_file_system(final_node, initial_node, reference_node, config_values) -> float:
+def score_node_file_system(
+    final_node: NodeUnion, initial_node: NodeUnion, reference_node: NodeUnion, config_values: "TrainingConfig"
+) -> float:
     """
     Calculates score relating to the file system state of a node.
 
diff --git a/src/primaite/links/link.py b/src/primaite/links/link.py
index f61281cd..145de5f3 100644
--- a/src/primaite/links/link.py
+++ b/src/primaite/links/link.py
@@ -8,7 +8,7 @@ from primaite.common.protocol import Protocol
 class Link(object):
     """Link class."""
 
-    def __init__(self, _id, _bandwidth, _source_node_name, _dest_node_name, _services):
+    def __init__(self, _id: str, _bandwidth: int, _source_node_name: str, _dest_node_name: str, _services: str) -> None:
         """
         Initialise a Link within the simulated network.
 
@@ -18,17 +18,17 @@ class Link(object):
         :param _dest_node_name: The name of the destination node
         :param _protocols: The protocols to add to the link
         """
-        self.id = _id
-        self.bandwidth = _bandwidth
-        self.source_node_name = _source_node_name
-        self.dest_node_name = _dest_node_name
+        self.id: str = _id
+        self.bandwidth: int = _bandwidth
+        self.source_node_name: str = _source_node_name
+        self.dest_node_name: str = _dest_node_name
         self.protocol_list: List[Protocol] = []
 
         # Add the default protocols
         for protocol_name in _services:
             self.add_protocol(protocol_name)
 
-    def add_protocol(self, _protocol):
+    def add_protocol(self, _protocol: str) -> None:
         """
         Adds a new protocol to the list of protocols on this link.
 
@@ -37,7 +37,7 @@ class Link(object):
         """
         self.protocol_list.append(Protocol(_protocol))
 
-    def get_id(self):
+    def get_id(self) -> str:
         """
         Gets link ID.
 
@@ -46,7 +46,7 @@ class Link(object):
         """
         return self.id
 
-    def get_source_node_name(self):
+    def get_source_node_name(self) -> str:
         """
         Gets source node name.
 
@@ -55,7 +55,7 @@ class Link(object):
         """
         return self.source_node_name
 
-    def get_dest_node_name(self):
+    def get_dest_node_name(self) -> str:
         """
         Gets destination node name.
 
@@ -64,7 +64,7 @@ class Link(object):
         """
         return self.dest_node_name
 
-    def get_bandwidth(self):
+    def get_bandwidth(self) -> int:
         """
         Gets bandwidth of link.
 
@@ -73,7 +73,7 @@ class Link(object):
         """
         return self.bandwidth
 
-    def get_protocol_list(self):
+    def get_protocol_list(self) -> List[Protocol]:
         """
         Gets list of protocols on this link.
 
@@ -82,7 +82,7 @@ class Link(object):
         """
         return self.protocol_list
 
-    def get_current_load(self):
+    def get_current_load(self) -> int:
         """
         Gets current total load on this link.
 
@@ -94,7 +94,7 @@ class Link(object):
             total_load += protocol.get_load()
         return total_load
 
-    def add_protocol_load(self, _protocol, _load):
+    def add_protocol_load(self, _protocol: str, _load: int) -> None:
         """
         Adds a loading to a protocol on this link.
 
@@ -108,7 +108,7 @@ class Link(object):
             else:
                 pass
 
-    def clear_traffic(self):
+    def clear_traffic(self) -> None:
         """Clears all traffic on this link."""
         for protocol in self.protocol_list:
             protocol.clear_load()
diff --git a/src/primaite/nodes/active_node.py b/src/primaite/nodes/active_node.py
index f86f818b..b73f80f0 100644
--- a/src/primaite/nodes/active_node.py
+++ b/src/primaite/nodes/active_node.py
@@ -24,7 +24,7 @@ class ActiveNode(Node):
         software_state: SoftwareState,
         file_system_state: FileSystemState,
         config_values: TrainingConfig,
-    ):
+    ) -> None:
         """
         Initialise an active node.
 
@@ -60,7 +60,7 @@ class ActiveNode(Node):
         return self._software_state
 
     @software_state.setter
-    def software_state(self, software_state: SoftwareState):
+    def software_state(self, software_state: SoftwareState) -> None:
         """
         Get the software_state.
 
@@ -79,7 +79,7 @@ class ActiveNode(Node):
                 f"Node.software_state:{self._software_state}"
             )
 
-    def set_software_state_if_not_compromised(self, software_state: SoftwareState):
+    def set_software_state_if_not_compromised(self, software_state: SoftwareState) -> None:
         """
         Sets Software State if the node is not compromised.
 
@@ -99,14 +99,14 @@ class ActiveNode(Node):
                 f"Node.software_state:{self._software_state}"
             )
 
-    def update_os_patching_status(self):
+    def update_os_patching_status(self) -> None:
         """Updates operating system status based on patching cycle."""
         self.patching_count -= 1
         if self.patching_count <= 0:
             self.patching_count = 0
             self._software_state = SoftwareState.GOOD
 
-    def set_file_system_state(self, file_system_state: FileSystemState):
+    def set_file_system_state(self, file_system_state: FileSystemState) -> None:
         """
         Sets the file system state (actual and observed).
 
@@ -133,7 +133,7 @@ class ActiveNode(Node):
                 f"Node.file_system_state.actual:{self.file_system_state_actual}"
             )
 
-    def set_file_system_state_if_not_compromised(self, file_system_state: FileSystemState):
+    def set_file_system_state_if_not_compromised(self, file_system_state: FileSystemState) -> None:
         """
         Sets the file system state (actual and observed) if not in a compromised state.
 
@@ -166,12 +166,12 @@ class ActiveNode(Node):
                 f"Node.file_system_state.actual:{self.file_system_state_actual}"
             )
 
-    def start_file_system_scan(self):
+    def start_file_system_scan(self) -> None:
         """Starts a file system scan."""
         self.file_system_scanning = True
         self.file_system_scanning_count = self.config_values.file_system_scanning_limit
 
-    def update_file_system_state(self):
+    def update_file_system_state(self) -> None:
         """Updates file system status based on scanning/restore/repair cycle."""
         # Deprecate both the action count (for restoring or reparing) and the scanning count
         self.file_system_action_count -= 1
@@ -193,14 +193,14 @@ class ActiveNode(Node):
             self.file_system_scanning = False
             self.file_system_scanning_count = 0
 
-    def update_resetting_status(self):
+    def update_resetting_status(self) -> None:
         """Updates the reset count & makes software and file state to GOOD."""
         super().update_resetting_status()
         if self.resetting_count <= 0:
             self.file_system_state_actual = FileSystemState.GOOD
             self.software_state = SoftwareState.GOOD
 
-    def update_booting_status(self):
+    def update_booting_status(self) -> None:
         """Updates the booting software and file state to GOOD."""
         super().update_booting_status()
         if self.booting_count <= 0:
diff --git a/src/primaite/nodes/node.py b/src/primaite/nodes/node.py
index 9fd5b719..cd500c9e 100644
--- a/src/primaite/nodes/node.py
+++ b/src/primaite/nodes/node.py
@@ -38,40 +38,40 @@ class Node:
         self.booting_count: int = 0
         self.shutting_down_count: int = 0
 
-    def __repr__(self):
+    def __repr__(self) -> str:
         """Returns the name of the node."""
         return self.name
 
-    def turn_on(self):
+    def turn_on(self) -> None:
         """Sets the node state to ON."""
         self.hardware_state = HardwareState.BOOTING
         self.booting_count = self.config_values.node_booting_duration
 
-    def turn_off(self):
+    def turn_off(self) -> None:
         """Sets the node state to OFF."""
         self.hardware_state = HardwareState.OFF
         self.shutting_down_count = self.config_values.node_shutdown_duration
 
-    def reset(self):
+    def reset(self) -> None:
         """Sets the node state to Resetting and starts the reset count."""
         self.hardware_state = HardwareState.RESETTING
         self.resetting_count = self.config_values.node_reset_duration
 
-    def update_resetting_status(self):
+    def update_resetting_status(self) -> None:
         """Updates the resetting count."""
         self.resetting_count -= 1
         if self.resetting_count <= 0:
             self.resetting_count = 0
             self.hardware_state = HardwareState.ON
 
-    def update_booting_status(self):
+    def update_booting_status(self) -> None:
         """Updates the booting count."""
         self.booting_count -= 1
         if self.booting_count <= 0:
             self.booting_count = 0
             self.hardware_state = HardwareState.ON
 
-    def update_shutdown_status(self):
+    def update_shutdown_status(self) -> None:
         """Updates the shutdown count."""
         self.shutting_down_count -= 1
         if self.shutting_down_count <= 0:
diff --git a/src/primaite/nodes/node_state_instruction_green.py b/src/primaite/nodes/node_state_instruction_green.py
index 7ebe3886..5a225c25 100644
--- a/src/primaite/nodes/node_state_instruction_green.py
+++ b/src/primaite/nodes/node_state_instruction_green.py
@@ -1,5 +1,9 @@
 # Crown Copyright (C) Dstl 2022. DEFCON 703. Shared in confidence.
 """Defines node behaviour for Green PoL."""
+from typing import TYPE_CHECKING, Union
+
+if TYPE_CHECKING:
+    from primaite.common.enums import HardwareState, NodePOLType, SoftwareState
 
 
 class NodeStateInstructionGreen(object):
@@ -7,10 +11,10 @@ class NodeStateInstructionGreen(object):
 
     def __init__(
         self,
-        _id,
-        _start_step,
-        _end_step,
-        _node_id,
+        _id: str,
+        _start_step: int,
+        _end_step: int,
+        _node_id: str,
         _node_pol_type,
         _service_name,
         _state,
@@ -30,9 +34,10 @@ class NodeStateInstructionGreen(object):
         self.start_step = _start_step
         self.end_step = _end_step
         self.node_id = _node_id
-        self.node_pol_type = _node_pol_type
-        self.service_name = _service_name  # Not used when not a service instruction
-        self.state = _state
+        self.node_pol_type: "NodePOLType" = _node_pol_type
+        self.service_name: str = _service_name  # Not used when not a service instruction
+        # TODO: confirm type of state
+        self.state: Union["HardwareState", "SoftwareState"] = _state
 
     def get_start_step(self):
         """
diff --git a/src/primaite/nodes/passive_node.py b/src/primaite/nodes/passive_node.py
index afe4e2d1..c79636e3 100644
--- a/src/primaite/nodes/passive_node.py
+++ b/src/primaite/nodes/passive_node.py
@@ -16,7 +16,7 @@ class PassiveNode(Node):
         priority: Priority,
         hardware_state: HardwareState,
         config_values: TrainingConfig,
-    ):
+    ) -> None:
         """
         Initialise a passive node.
 
diff --git a/src/primaite/nodes/service_node.py b/src/primaite/nodes/service_node.py
index 4ad52a1e..ef0cd92e 100644
--- a/src/primaite/nodes/service_node.py
+++ b/src/primaite/nodes/service_node.py
@@ -25,7 +25,7 @@ class ServiceNode(ActiveNode):
         software_state: SoftwareState,
         file_system_state: FileSystemState,
         config_values: TrainingConfig,
-    ):
+    ) -> None:
         """
         Initialise a Service Node.
 
@@ -52,7 +52,7 @@ class ServiceNode(ActiveNode):
         )
         self.services: Dict[str, Service] = {}
 
-    def add_service(self, service: Service):
+    def add_service(self, service: Service) -> None:
         """
         Adds a service to the node.
 
@@ -102,7 +102,7 @@ class ServiceNode(ActiveNode):
                     return False
         return False
 
-    def set_service_state(self, protocol_name: str, software_state: SoftwareState):
+    def set_service_state(self, protocol_name: str, software_state: SoftwareState) -> None:
         """
         Sets the software_state of a service (protocol) on the node.
 
@@ -131,7 +131,7 @@ class ServiceNode(ActiveNode):
                 f"Node.services[<key>].software_state:{software_state}"
             )
 
-    def set_service_state_if_not_compromised(self, protocol_name: str, software_state: SoftwareState):
+    def set_service_state_if_not_compromised(self, protocol_name: str, software_state: SoftwareState) -> None:
         """
         Sets the software_state of a service (protocol) on the node.
 
@@ -158,7 +158,7 @@ class ServiceNode(ActiveNode):
                 f"Node.services[<key>].software_state:{software_state}"
             )
 
-    def get_service_state(self, protocol_name):
+    def get_service_state(self, protocol_name: str) -> SoftwareState:
         """
         Gets the state of a service.
 
@@ -169,20 +169,20 @@ class ServiceNode(ActiveNode):
         if service_value:
             return service_value.software_state
 
-    def update_services_patching_status(self):
+    def update_services_patching_status(self) -> None:
         """Updates the patching counter for any service that are patching."""
         for service_key, service_value in self.services.items():
             if service_value.software_state == SoftwareState.PATCHING:
                 service_value.reduce_patching_count()
 
-    def update_resetting_status(self):
+    def update_resetting_status(self) -> None:
         """Update resetting counter and set software state if it reached 0."""
         super().update_resetting_status()
         if self.resetting_count <= 0:
             for service in self.services.values():
                 service.software_state = SoftwareState.GOOD
 
-    def update_booting_status(self):
+    def update_booting_status(self) -> None:
         """Update booting counter and set software to good if it reached 0."""
         super().update_booting_status()
         if self.booting_count <= 0: