Thursday, March 12 2015
The most important aspect of naval artillery
To obtain a targeting solution on an enemy ship there are three variables: target speed, target course, and range to the target. It takes about three minutes to obtain a reasonably accurate calculation of a target’s course and speed mathematically. Sometimes ships used quicker methods (eyeballing the course and estimating speed based on the bow wake of the target) in an emergency, but that sort of accuracy depends on the skill and experience of the targeting crews.
Before radar, obtaining the range to a target was the most difficult of the variables. In this regard, the US Navy had a distinct advantage over the Japanese because the first mention of the Japanese using radar on ships wasn’t until 1944. Still, there are numerous variables relating to the atmospherics that could affect range accuracy, especially at long range. Naval gunners assumed a few salvos would be required to obtain the correct effective range to the target.
Gunners used one of two methods to obtain the proper effective range: laddering and bracketing. Gun crews used laddering at longer ranges. When using laddering, ships would deliberately fire their first salvo short of the target and then increase the range until the shots fell on the far side of the target. Once the shots fell long, gunners could make a final attempt to obtain the correct effective range.
Using the bracketing technique, ships would observe the hits from their first salvo. If the shot landed long, the ship would try to make the next salvo short and vice versa. With one shot long and one shot short, spotters would estimate the distance between the shell impact points and interpolate to obtain the range to target.
One interesting aspect of bracketing is the target ship can almost estimate where the next shot will fall. Readers will see O’Toole using this in Vows to the Fallen. During World War II, US ship captains got into the habit of changing course so their range from the enemy would be the range of the last shot fall. When the enemy adjusted their range and fired again, their shells would fall at the range the US ship was before it had changed course. The common thing to do was to steer for the last shell impact point. As you can guess, this could result in a guessing game between ships.