37x122mmR weapons and flares date back to before 1914, some stocked but most pistol style. With a little imagination such launchers could have been used in WW1 for explosive and chemical rounds.Federal Gas Gun https://en.wikipedia.org/wiki/Federal_Riot_Gun was available in early 1930's. I am amazed the USMC did not make use of this in Central America. Also, once rifle grenades were devised, I wonder why the leap to a large shotgun based grenade launcher was ignored.
Gas rounds were available in 26.5x103mmR (the 1" flare round) before WW1 (by 1912 at the latest) and used by the French army (to little effect) in 1914. The principal filler was ethyl bromoacetate, replaced by chloroacetone. The rounds were too small to have much effect.
The Manville Machine Gas Projector was developed in 1935 first sold in 1938; this was a bulky, short-barrelled, revolver launcher in 26.5mm with an eighteen-round cylinder. A 12-gauge version (intended for muzzle blast tear gas and rubber pellets but entirely capable for firing shot and slug) was also sold. It held 24 rounds but saw even more limited use than the 1" version (for a start it was a SBS under the NFA). While some sources (e.g. Wiki) claim a twelve-shot version was manufactured in 37mm, I am personally very dubious about this; most sources don't mention it and they many be conflating such a weapon with the much later MM-1 (developed around 1970). Of course Manville may have developed a prototype in this calibre.
The projector saw very few sales, it was expensive, heavy and very slow to reload.
Both Britain and Germany used the 1.5" Maxim ("one-pounder") to a very limited extent. However the 37x94mmRround was considered ineffectively small by both sides and against British doctrine as an infantry weapon.Also, Vickers 1 pounder and 1 inch automatic cannon, Fiat Revelli 25mm cannon, COWS and Davis guns, and Becker cannons all were able to fill the short to medium range direct fire role by WW1. No one thought to drag these into the trenches.
France and the USA used the French designed APX Mle 1916TRP[1] as a (relativity) portable infantry anti-fortification weapon. It fired the same 37x94mmR cartridge as the "pom pop" but was a far lighter (about 40kg[1] for the gun alone as against 200kg for the 1.5" Maxim) and was a single-shot. Standard crew was seven.
Hope this helps.
[1] Canon d’Infanterie Modèle 1916 Tir Rapide, Puteaux. Infantry gun model 1916, quick-fire, designed at Puteaux arsenal
[2] The tripod mount broke down into two parts, 40kg and 28kg. A 20kg gunshield was also available