A very teensy weensy expansion kit that contains 20 chipboard tokens with 2 new rule systems:
DIVED SUBMARINES
The Dived Submarine side is used to mark Submarines that escaped
combat by diving after they are returned to the World Map. These escaped dived subs can then avoid pinning and immediately move to an adjacent sea region.
CONVOY CASUALTIES
The Convoy Casualty side is used to mark sunk convoy ships on the
Morale Board. Each sunk convoy is worth 6 casualty points.
See here for full rules:
https://drive.google.com/file/d/1eem2_VV7UsfgDkbDCxkLCQLIE4fVmkos/view