In Twenty-Two on Peliliu, his memoir of service in the Great Pacific War, US Marine George Peto recalls the building, from locally-available elements, a shoulder-fired 60mm mortar.
Using good old American know-how, our own guys were trying to rig some kind of a mortar weapon that could be shoulder-fired, like those weapon-development idiots were doing back in the States. For that reason, one day, our battalion armorer took a spare 60mm mortar and rigged a stock for it, with a trigger to a firing-pin device. After making sure that it was all securely attached and hooked up, our company was asked to try out the new weapon.
Whoever fired it would probably have to be braced for quite a kick. So Ernie Huxel, the gunner for the Number Three 81mm mortar, was the guy we chose to fire it, because he was one of the burliest guys in the platoon, with muscles all over the place. A few of us went with him out to an open area for the trial test-firing. After some instruction by the armorer and some joking around, Huxel grabbed the weapon and got down into a prone position. After checking everything out once more, he carefully aimed the weapon and then fired it.
It went off with a loud cough, and sure enough, the recoil of the damn thing was tremendous, especially because Ernie was in a prone position. Therefore, his entire body was behind the weapon, so his shoulder absorbed the full force of the kick. The whole mortar whirled up out of Ernie’s hands, went sailing into the air, twirled around, and fell back onto the ground with a clanking thud. Ernie was thrown back and rolled over on the ground, groaning, clearly in distress. We could tell that he was hurt. It’s a wonder the damn thing did not break his shoulder.
So much for innovation.
Sources
George Peto (with Peter Margoulis) Twenty-Two on Peleliu: Four Pacific Campaigns with the Corps, The Memoirs of an Old Breed Marines (Havertown: Casemate, 2017) pages 173-174
The photo, which is taken from footage filmed during the battle, shows Marines employing a government issue shoulder-fired mortar, either the Mark I Mod 0 of the US Navy Bureau of Ordnance or the T20 of the US Army Ordnance Department.
For Further Reading
Having been the Chief Instructor of Weapons at The Infantry Training School at Camp Geiger pre SOI, nothing, absolutely nothing would surprise or amaze me about Marines and weapons innovation! Okay so mortar bazooka didn’t quite work out! They were trying to figure out a way to get more suppressing fires outbound! Always a great goal!
I've never had the opportunity to try it myself but some SNCO mentors of mine once shared a collection of techniques they had experimented with for using the 60mm mortar in direct fire mode. As far as I know, there are some doctrinally approved methods like the use of a "knee plate" (the name is misleading because it does NOT sit on your knee) or other modified baseplates but they offer limited accuracy. One NCO said he achieved better results by using one of these smaller/modified baseplates braced against a large tree. However since my knowledge is only second hand I would be interested to hear if anyone else has experience or opinions on whether these options are effective.