We've written bits and pieces about the light machine guns in Isonzo (as distinct from the heavy machine guns which are static weapons placed by the map designers) but never brought them all together. If you haven't tried them out, you can unlock them by completing Assault class missions.

German MG 08/15

The German faction was added to Isonzo way back in December 2022, and they brought with them the third light machine gun to feature in the game: the Maschinengewehr 08 / 15, or MG 08/15 for short. It's an adjusted version of the basic MG 08 heavy machine gun, which is itself based off the original Maxim gun from 1884.
The MG 08/15 was first used in 1917 during the Second Battle of the Aisne on the Western Front. Overall it did the job, but was never an excellent weapon. It was heavy compared to the French Chauchat LMG, with the water cooling system compounding the issue. Fortunately in Isonzo you don't have to carry it all the way to the frontline.
In Isonzo the MG 08/15 is limited to the German Assault class, and within that class limited to a maximum of 2 users at a time. These limitations also apply to the machine guns used by the Italian and Austro-Hungarian Assault classes. Even with the need to deploy for accurate fire, light machine guns are extremely powerful weapons so it makes gameplay sense to limit their employment. At the same time, they were historically limited, even with increasing German efforts to equip their troops with more light machine guns. For example, a German company would have around 240 men, and by 1918 with a full complement, each company would have 6 MG 08/15s. From that perspective, having 2 LMGs available for the 24 German soldiers in a match is generous - as you might expect for the assault troops in the thick of the action. An interesting fact: the gun lives on in the German dialect, with nullachtfnfzehn being colloquially used to refer to something that's entirely average and unremarkable.

The MG 08/15 in Verdun

The MG 08/15 appeared in our first game, Verdun! They could be used by machine gunners in the Landser and Schtzen squads. Verdun also had the rarer MG15n.A. and MG08/18 light machine guns.
An MG 08/15 in Verdun.

Italian Villar Perosa

We've written about the Villar Perosa before, in one of the earliest Isonzo Dev Diaries: https://steamcommunity.com/games/1556790/announcements/detail/4986028794973970851?snr=2___
A fascinating weapon with a distinctive double barrel design (actually two entire firing mechanisms coupled together) it was intended to be an aircraft weapon as well as a man-portable gun. It wasn't so effective in the air, but served well with ground troops. Technically it could be considered a submachine gun because it fires handgun cartridges instead of rifle cartridges.

Austro-Hungarian Madsen

The Austro-Hungarian Assault class makes use of the Madsen, a Danish light machine gun that was used around the world into the Second World War and beyond. When the First World War broke out, Austria-Hungary was not in a position to develop their own light machine gun, so they acquired Madsens from their German allies - these may well have been Brazilian 1907 Madsens, possibly heisted on their way back to Denmark for improvements. Nothing is certain, but a shipment of Brazilian Madsens did go missing and a number of matching weapons did show up in Central Powers service.

While mass production of the Madsen began in 1902 (and continued until 1955), the design process started back in the late 1880s with Danish artillery officer Captain Vilhelm Herman Oluf Madsen attempting to create a self loading rifle with the help of Danish Arsenal technician Rustmester Rasmussen. However, Captain Madsen left to become the Danish Minister of War before the Madsen machine gun was invented - credit for that should go to a Lieutenant Jens Schouboe, who patented it in 1901.

Stay (air or water) cooled out there, machine gunners.