How did submarines find targets?

Submarines had various ways to find targets during WW2. One was just to search in the area they were given to patrol. It would be up to the captains to try to determine the most likely areas for successful hunting. That would be based on their own experience, information from other captains in patrol reports and general intelligence information.

If enemy shipping had gotten past another American submarine, that boat would broadcast the location and best estimate of base course and speed. That would hopefully allow other boats to get into position to attack.

We began to formally use wolfpacks in the fall of 1943.  Now submarines were working together to identify the most likely routes for enemy shipping and to plan coordinated attacks. Once ships were sighted, then the wolfpack boats executed their attack plans while not endangering each other.

The captains also applied their own analysis to all the information they had and make their best estimate of what the enemy could do and might do. For example, if a captain had been successful in a particular area, he might estimate that for the next few days, at least, enemy shipping might be routed away from him. Where they might go could be limited by geography, likely shelters or ports, etc.

Note: Two of the best books that provide insight into the thinking of our captains are “Thunder Below” by Gene Fluckey and “Clear the Bridge” by Richard (Dick) O’Kane.

Or, perhaps as the Batfish found, there could be more Japanese ships passing along the same route and they should quietly stay in that area. In the case of the Batfish, the targets were submarines.  Batfish simply remained where they had just sunk one Japanese boat and claimed two more over the next 72 hours.

Note: One book on the Batfish is “In the Course of Duty – The Heroic Mission of the USS Batfish” by Don Keith.

There were also the “Ultra” or “Magic” messages. These contained information provided to the captains based on our intercepts of Japanese messages. We had broken most of the Japanese naval codes. If we could decipher the message in time, we could provide the information to captains helping them to intercept and attack the ships. However, the captains could only guess at the source of the intelligence.

Then there was just plain luck. An enemy vessel might just happen to be transiting through the boat’s assigned area. In that case, the crew had to be looking for clues that targets might be nearby. Radar might have picked up unidentified contacts. (The use of radar was often limited to avoid giving away one’s own location.) Other methods were sighting smoke on the horizon and hearing propellor sounds through sonar. It might even be possible to notice an aircraft in the distance flying circle patterns that could be protective cover for a convoy.