I always hear about ships zig-zagging in WWII in order to avoid submarines. I’ve never really understood why. To me it would make most sense to steam as straight of a line as possible in order to minimize the amount of time on the sea, and thus your exposure. Obviously you wouldn’t have every ship take the exact same path otherwise subs will just sit in the path. I have three theories to why zig-zagging was instituted:
(1) It was less complicated than assigning a ship a random straight path to take. Ships would be zig-zagging around the most direct route between the two ports. While enemy subs would generally know where the ships were, they would never be able to know exactly.
(2) Zig-zagging makes it harder for a sub to hit them with a torpedo. It takes time to get a firing solution, and it takes some time for the torpedo to go between the sub and the ship. If you are randomly turning there is a chance that you would turn out of the path of the torpedo.
(3) Zig-zagging makes it impossible to radio ahead your path. It’s impossible to project the path of a randomly zig-zagging ship. Thus the enemy would not be able to figure out that you would be at position X in 2 hours, and would not be able to lay an ambush.
1 just doesn’t make a whole lot of sense to me. It’s not that complicated to switch up your route. 2 doesn’t make sense either because it seems like a bad decision to waste time zig-zagging for the small chance of getting lucky. 3 makes the most sense, but wouldn’t the enemy be able to observe the ship and get an average direction out of the zig-zagging?