You have solved this problem:
https://www.matrixgames.com/forums/tm.asp?m=4780265
But, on UK side, they have Interceptors 1942 whereas this is not yet discovered. We really need the Advancements report to clean up all sides / all scenarios.

Moderator: AlvaroSousa

Supply Convoy Interdiction – After supply is calculated for a port, friendly and enemy fleets are automatically calculated for interdicting the supply line. Port supplies can be affected by enemy naval and air forces in the area with at least 1 operation point at the end of the turn. Naval forces need to be within 4 hexes and enemy air forces within 8 hexes, or less if the air unit range is less, of the port to have a chance to affect supply delivered. Friendly air and naval forces automatically escort within the same ranges. Port levels can’t be reduced lower than 1. The further away an interdicting enemy fleet is from the enemy port, the less chance the fleet has to interdict the supplies. There is a small chance a transport point will get sunk if the supply convoy is interdicted. Escorts have no such penalty as they are considered as being with the supply transport coming into the port.



Supply Convoy Interdiction – After supply is calculated for a port, friendly and enemy fleets are automatically calculated for interdicting the supply line. Port supplies can be affected by enemy naval and air forces in the area with at least 1 operation point at the end of the turn.
Naval forces need to be within 4 hexes and enemy air forces within 8 hexes, or less if the air unit range is less, of the port to have a chance to affect supply delivered.
Friendly air and naval forces automatically escort within the same ranges. Port levels can’t be reduced lower than 1. The further away an interdicting enemy fleet is from the enemy port, the less chance the fleet has to interdict the supplies. There is a small chance a transport point will get sunk if the supply convoy is interdicted. Escorts have no such penalty as they are considered as being with the supply transport coming into the port.

