Once your sub had had its shot, and the enemy escort knows you are out there, it’s time to get out of Dodge. You have two basic choices - get out on the surface, or get out underwater.
On the Surface
Usually this is the end result of a night surface attack, but not necessarily. Speed and confusion are your friend. Use them. The more chaos you have caused up til now, the better. The big danger with a surface exit is a shot from one of the escorts penetrating the hull. Submarines have so little reserve buoyancy that one hit in the hull will sink the boat. The big benefit is speed. Surfaced speed on the diesels is so much faster than underwater speed that sometimes it is worth the risk.
Japanese Escort Guns
Japanese escorts had guns ranging from 3 inch on frigates to 4 inch on covettes to 5 inch on destroyers. Cruisers in a battle group would have 6 or 8 inch guns.
A favorite tactic for larger escorts is ramming. Destroyers have a heavy sharp bow that can crush through a sub hull like paper. Mid-sized corvettes were known to do this also. Small frigate-type escorts had neither the mass nor structural strength to ram. A rammed sub is destroyed.
Japanese naval lookouts are very good, and their optical equipment is superb. Rate them at +4, with an endurance of 9.
Night Modifiers are -2 Large for dark nights, -1 Large for bright nights.
Chaos Modifiers are given by the GM, and should range from +0 for a bungled attack to -2 for a devastating attack.
For most of the war, this was the preferred method of escape until night surface attacks came into vogue in mid 1944. In this, the submarine attempts to creep away silently underwater after the shot. The faster the sub moves, the more easily it can be detected - 0-2 knots -1 Small Modifier, 3-4 knots +0, 4-5 knots +1, 6-7 knots +2, 8 knots +3, 9 knots +4 Small Modifiers.
Japanese Escort SONAR
Japanese SONAR was fair, though not as good as American equipment. Effectively, rate Japanese SONAR at Acquisition +2 to locate the sub. An escort needs 3 successes to lock the submarine, in which case depth charges have a +1 chance. If SONAR gets only 1 or 2 successes, the escorts can only get a general area reading with hydrophones, with the depth charges at standard effectiveness. If no successes are rolled, the sub escapes. Once SONAR is rolled, it is not re-rolled until the situation changes.
A sub can go to Silent Running mode, in which all pumps and AC is shut down. This gives a -1 Small Modifier to be detected. For each hour is Silent Running mode, all crew END goes down by 1, due to increasing heat and no ventilation.
By accelerating fast underwater, then making a sharp turn, the submarine can create a hard “knuckle” of turbulent water in the wake of the sub, whereupon the sub rapidly slows to creeping speed.
The “knuckle” will reflect SONAR pings as if it were a sub underwater for several minutes. The Diving Officer needs to make a Tactics check when attempting to create the “knuckle”. Each success gives a Small Modifier penalty for the escort’s SONAR Acquisition check. On a failure, the escort will depth charge the “knuckle, letting the submarine escape.
A knuckle can also be created on diving from the surface.
There may be a thermocline - a layer of water at a very different temperature than the layer above it - which can reflect SONAR pings. The escort has -3 Small Modifiers to success in Acquiring a sub under the thermocline - if such a themocline exists.
A thermocline can be located by the sub’s Signals Officer with a successful Acquisition check and 3 or more successes.