Actually a game and a scenario module. Convoy is the quick-play rules heavily based on Command at Sea (WWII module of the Admiralty Trilogy). Deadly Waters is a scenario package.
Convoy takes the Admiralty Trilogy-Command at Sea (CaS) system and “simplifies” it through an extensive use of tables that lay out most of the interactions (sighting, combat, etc) that are in CaS but often need to be figured on-the-fly. The greatest change from the CaS system is damage resolution; whereas CaS uses a Damage Points/Critical Hit system Convoy uses a hit system that emphasizes the character/type of damage. Again, Convoy has in effect “tablefied” the CaS system. The result is a faster playing system since most of the lookups are moved to pre-made Combat Cards or tables.