In Viet Bnam era movies, the use of the mortar cannon by ground troops is shown almost as much as the M-16. The soldier drops a round in the mortar, then FOOMP off it goes and he drops another one in. FOOMP.
My question, how safe were these? Did rounds ever blow up in the cannon? Fail to launch? Hang fire? Or could you just shove rounds through it all day until your arms got tired and never worry?
Doesn’t look like the statistics show the precise type of weapon causing a death in the “accidental self-destruction” column, and if you weren’t the one causing the accident, apparently it would be “accidental homicide”. But mortars are definitely not idiot proof.
This thread from a couple of years ago was started about a recent mortar accident:
https://boards.straightdope.com/sdmb/showthread.php?t=825419
They have occurred in fairly recent years so are still possible.
This paper analyzes mortar accidents specifically in the US military in Vietnam era
https://apps.dtic.mil/dtic/tr/fulltext/u2/893104.pdf
It does not give statistics of how frequently they occurred but rather deals with particular causes of actual detonation of either a round’s explosive charge in the barrel, or more than one propelling charge, IOW things that could make the mortar burst and kill or injure crewmen. Since a relatively small number of actual incidents are mentioned it can be inferred that this wasn’t extremely common, but common enough to analyze how it could be reduced.
One thing mentioned in the thread and paper is double loading, one round is dropped in, it ‘whooshes’ but does not ‘foomp’ (actually a theme of an episode of ‘Gomer Pyle’) but another round is loaded on top, or just two people are loading to get maximum firing rate and the second loader drops in a round before the other loader’s round gets to the bottom of the tube. That was harder in mortars with mechanical devices to prevent it (some Soviet mortars used by the other side in the Vietnam War had those). As the paper describes in detail though this would not necessarily cause a disaster because the fuze of the round on bottom still had its bore riding safety pin which would only eject when it emerged from the muzzle. But, they found that protruding rivets on the noses of some contemporary models of fuze would activate the propellant primer of the second round acting like the mortar’s firing pin, which would either jam the first round down on the actual firing pin and activate its propellant after all, and/or the propellant gases of the second round would penetrate the first round’s fuze and set off if its bursting charge despite the safety pin still being in place. Without the protruding rivet however, the second round might just lodge against the first and neither fire.
And other mechanisms of disaster are described, like the round was dropped on the ground after removing the safety wire but before loading. That would not make it go off generally, but it might eject the bore riding safety pin. Then the fully armed fuze might be initiated in-bore by firing the round. Or, flaws in the round’s explosive charge could make it sensitive to detonating in-bore on firing.
Various of these specific mechanisms are less likely with modern mortar rounds and fuzes with electronic safety devices and higher quality control. But they are still not impossible.
Of course disasters have occasionally happened and can happen with breechloading artillery too.
Mortars were pretty heavily used all the way back since WWI (and actually before then), and they didn’t have a reputation for blowing up in everyone’s face. That doesn’t mean that they were 100 percent safe and you never had to worry about them though.
There are a lot of ways that they can fail. They can fail to launch and blow up inside the tube. They can only partially launch and blow up in mid-air right above the tube, or they can just flop out of the tube and blow up on the ground. The round can detonate early, so it could launch correctly but still blow up just as it leaves the tube, for example.
If you are attempting to drop rounds through it all day until your arms get tired, then the weapon gets very hot, and now you have a danger of a cook-off, which is basically the round exploding due to the heat, usually while still in the tube.
Another danger in the heat of battle is that you might not be able to hear the FOOMP over the sounds of all of the gunfire and explosions all around you. So what happens if the weapon doesn’t fire? You don’t hear any FOOMP but you might not have heard the FOOMPs all day long so you wouldn’t notice. You drop a second round in on top of the first, and the first round explodes, killing you and everyone nearby. Even if you aren’t in battle, soldiers get trained to where they operate like robots, just constantly going through the motions of firing shell after shell. Sometimes in training the round won’t go off, and the soldier loads the next round without even stopping to think, often with tragically fatal results.
There were a lot of mortar systems used in Vietnam, but I think the most common were the M2 and the M29. The M2 had been in service since WWII and the M29 had been in service since before the Korean war. The good thing about using older systems like this is that since they have been around for a while, they usually have all of the kinks worked out of them and they work fairly reliably.
The thing to remember is there isn’t all that much to a mortar. There’s a tube with a firing pin on the bottom, a base plate, and legs with the aiming mechanism. The majority of the technology is in the round.
Thanks, all, for the replies!
Here’s a short compilation video of 10 mortar failures.
I looks to me like all but one of them were due to munition malfunctions.
How would that work? From the videos I’ve seen, the rounds spend less than a second in the tube. Even if the tube was hundreds of degrees it seems like there is not enough time for the heat to transfer into the round and heat up any explosives.
Could it be that the steel tube heats up enough to weaken it and the FOOMP actually breaks the tube and sends shrapnel into personnel sitting beside it?
They are quite safe. The biggest danger is dropping the bomb into the tube and then moving away quickly. If you take your hand back over the mouth of the barrel you can lose your hand. There are a number technical fixes to this, but training works well too.