Thursday, March 05 2015
How long does the enemy ship have to get out of the way?
Hollywood movies sometimes portray incoming projectiles by the sound they make as they scream overhead, but I have yet to see a movie that exposes the problems created by projectile flight times. For example, if a five-inch gun fires at a target ship at 10,000 yards (five nautical miles) away, and the target ship is traveling at thirty knots, the target ship would move more than the length of three football fields before the shell hits because the flight time of the shell would be twenty-two seconds. In Vows to the Fallen, readers will see how flight times can affect a battle.
The navy considered the destroyer’s five-inch guns as dual-purpose weapons usable against surface and air targets. Standard procedure was for destroyers to open fire on incoming aircraft at 9,000 yards. Even assuming flight times are linear with range, which they aren’t, the shell wouldn’t hit the aircraft for thirteen seconds at a range of about 6,000 yards.
Flight times get larger the greater the range and the larger the shell. Here are some example flight times for five, eight, and sixteen-inch projectiles.
Projectile flight times are important because the time a projectile is in flight is also the time the target ship has to evade. In a previous post on accuracy, I discussed how the probability of hitting the target depended on the target’s being cooperative and not changing course or speed while the projectile was in flight.
In the next post, I will cover targeting techniques and pull all of the artillery blogs together with a final post on rate of fire.