105mm HMMWV.

This is coolbert:

See previous blog entry the "soft recoil" indirect fire weapon. Not just a pie-in-the-sky mirage. Already in use.

"pie in the sky: noun - A fanciful notion; ludicrous concept; the illusory promise of a desired outcome that is unlikely to happen."

"Army Tries Out Humvee-Mounted Howitzer"

From https://breakingdefense.com | article SYDNEY J. FREEDBERG JR. | May 18, 2021.

"How do you safely fire a 105 mm cannon off the back of a Humvee? With a unique recoil-reduction system."

See the You Tube short video the American Humvee mounted howitzer:

Additionally:

"The Army [USA] is checking out two sizes of a unique low-recoil howitzer system: a 155mm gun on a 6×6 truck, Brutus, and a 105mm on a 4×4 Humvee, Hawkeye. That’s an extraordinarily small vehicle to mount an artillery piece, and reducing recoil is the key to making it work."

I can imagine there is merit to these 105 mm low-recoil artillery systems. You can proliferate the battlefield with greater numbers a much more mobile unit less susceptible to enemy counter-battery/counter-mortar fire.

All that additional weight of the tube firing piece will strain the Humvee too much? Wear and tear on engine, suspension, tires, transmission will greatly reduce the vehicle life-expectancy and usefulness.?

US Army going to go with self-propelled heavy artillery of the 155 mm variety. Shoot-of as deemed of proven systems with evaluation for future purpose or USA manufacturing under license underway even as we speak. 

coolbert.