so i was watching "Operation Petticoat" the other day which follows a US submarine which was lining up on a enemy tanker but the sub veered off course and fired its torpedo. The torpedo ran aground and hit an enemy truck and exploded. "Sighted tanker, sunk truck".

Although a fun scene, it's rather unlikely. Once out of the water, with nothing to propel it, a torpedo would rapidly stop.
Actually, it would ground well before hitting the beach; they typically ran 12 feet or more underwater.

true it would slow rapidly however wouldn't the inertia of something traveling nearly 60knts propel it far enough to hit the truck. if u watch the movie the truck is only about 20ft. from the water also u can see that it looks like a very gentle incline for the torpedo to leave the water.

Ever hit a sandbar with a boat doing 20 knots?

It stops. I would not want to be in a boat hitting a sandbar at 60 knots.......

It would be interesting to test out with a scale model though. The torpedo myth, that is.

The torpedo would be doing about 60knts. not the sub the may cruise at maybe 24knots

My point is: The torpedo would stop upon encountering the beach. Take a radio controlled boat and run it as fast as it can go in the water.......then run it on a beach. Inertia doesn't make the boat continue at it's water speed.

the impact with the beach would most likely detonate the explosives before it ever reached the truck (depending what it is loaded with)
also the enemy sub would have to be very fast to veer out of the way of a torpedo from a standstill.

Hunter8659 ,

what enemy submarine??????

might i just say that 1 a model boat does have the Mass of a torpedo and 2 it sure doesn't have the speed so really that was pretty much irrelevant i'm not saying it wouldn't slow down drastically all im saying is it might be able to travel the 20ft. to reach the truck.

Gotta loop back on this one - the most common submarine torpedos from WWII where the MK-14 model. Others were used later in the war, but the MK-14 was "the" torpedo.

The MK-14 had top speed of 46 kts. Assuming it was running at high speed, it is very likely it could run itself out of the water and up the beach purely on momentum. Remember that the torpedo is 21 feet long, so when the nose is up the beach, the propellor is still in the water. Also, 46 kts is about 50 mph...pretty fast.

The question becomes - will it explode?

The Mk-14 utilized 2 types of detonoation devices; magnetic and contact. The magnetic exploders were extremely unreliable and frequently could be set off by flux in the earth's magnetic field, detonating well before it reached the target. Because of the reliability, I think the magnetic exploders can be ruled out. They were usually turned off by skippers who had any experience with them.

The contact exploder worked by crushing the tip of the torpedo and driving a pin backwards (past a magnet?) to produce an electical impulse to set off the detonation. Would there still be enough force to crumple the tip of the nose cone and push the pin backwards? Unknown, but I find it implausible. It was designed to detonate against a ship's hull at around 30 kts, so if the torpedo has slowed down more than that, it probably just nudges the truck and does nothing.

If it was a US sub would the torp then would have the terribly unreliable fuse?
I recall tales of Japanese merchantmen turning up in port with a live torpedo stuck in the side of the hull.
something to do with updating the torpedo engine but not the impact pistol.
wouls that have any bearing on the myth?

In case it makes any difference, the US torpedo mechanical exploder used a fulminate of mercury capsule which was broken by the firing pin contacting the enemy ship and driving it back into the capsule with enough force to cause an explosion.

American contact exploders were unreliable in the early days of the war due to the fact that the impact would bend the heavy firing pins, thus not hitting the fulminate capsule.

After much experimentation at Pearl Harbor, the navy took old propellers of Japanese aircraft shot down during the raid and made firing pins that worked correctly. Thus, the Japanese navy should get credit for every ship sunk after mif 1943. Funny things, coincidences.

quote:

Originally posted by Pennsyjohn:
..., the navy took old propellers of Japanese aircraft shot down during the raid and made firing pins that worked correctly....

Pj, could you expand on this? I'm not following the connection between aircraft propellors and torpedo firing pins. Now you've got me curious.

quote:

Originally posted by Frequently Mythtaken:

quote:

Originally posted by Pennsyjohn:
..., the navy took old propellers of Japanese aircraft shot down during the raid and made firing pins that worked correctly....

Pj, could you expand on this? I'm not following the connection between aircraft propellors and torpedo firing pins. Now you've got me curious.

OK. The firing pin on the torpedo is a rod that extends from the head of the torpedo and goes into the exploder where it caused the hitting of the fulminate of mercury capsule. This is the way they devised to make the torpedo explode.

Newport Torpedo Station made the pin out of a steel that was too heavy. The inertia of the impact caused the pin to deform, and the torpedo did not explode. The story of Japanese ships coming into port with an American torpedo in their side was true.

Pearl Harbor Sub base experimented with firing torpedoes into a cliff side until they got one that did not explode. They (carefully) disassembled the warhead and found the problem.

They then proceeded to experiment with different metals in the hopes of finding one readily available to them until such time as they could get Newport to get correct ones made (Government bureaucracies have always been there).

One enterprising machinist went to the junkyard and got some old propellers from the Japanese planes shot down on December 7th. They were tested and found to work. As a result, for a period of time American submarines went on patrol with torpedo warheads with firing pins made from Japanese propellers.

If you really need more, I'll see if I can find the book I read that in. It is a history of submarine operations in WW II.