In 1955 with the reunification of Germany, and pressure from Germany, and fears of the Soviets using a weak neutral Germany to push communism further west, the Allied Powers agreed to allow the new German State to form its own army for defense, and maintenance of its neutrality. This was approved, with Germany being allowed to form its new army, which quickly began searching for equipment. One of its first actions, before the army was even properly set up, was to begin searching for a mainstay rifle. Many options were considered, including but not limited to the AK-47, the FN FAL, the M1 Garand, and the CEAM Modèle 1950. However, H&K offered a homegrown weapon, to be put up in competition as the "Gewehr Fünf" or G5. The FN FAL was designated as G1, being held over from the Bundesgrenzschutz, the AK47 being present as a holdover from the Volkspolizei. Other new rifles such as a variant of the Spanish CETME A2b were given their own designations, with the CETME rifle being given G3. However, in the end, the G5 would win out as the idea of a locally designed rifle was very tempting to many. This, combined with a few of the more hesitant judges finding reasons to support the G5, when they allegedly found themselves to have a sudden influx of cash was accepted as the mainline rifle of the new German Armed Forces. The magazine was found to be an issue, with the only versions available for it being a 20 round or 10 round magazine. However, the 20 round was considered adequate, as the lower weight of the rounds compared to many of its contemporaries allowed riflemen to carry more rounds. It quickly found itself to be popular with more neutral countries who did not want to associate with either the Eastern or Western Block but still wanted a reliable weapon to depend on.
In 1962, with increasing tensions around the world, the German Armed Forces were tense about any possible invasion and felt they would need to fight in-house to house combat, with specific strong points being what would make or break a battle. This thinking was informed by the combat at Stalingrad and in other cities, most famously with Pavlov's House. As such, it was ordered that a way to mount a small and portable flamethrower on the rifle be made. As such, the DM 35 Gewehrflammpatrone was made and ordered. In service, it was not extremely popular, as it was seen as non-practical. It was joked that it only had enough fuel to light a cigarette, and thus a nickname for the device became somewhat common the Feuerzeug, or the Lighter. The flamethrower would use a mixed gasoline-based compound, similar to napalm, making it highly effective at clearing out areas, but due to its limited size, it was expected to only be able to be used once.
In 1987, as the needs of armies changed, so did their role. In Lesotho, as the UN deployed to help keep the peace, German and South African forces found themselves in need of a way to breach houses easily. As such, soldiers began carrying shotguns, but these were too large to be easily carried by soldiers also keeping their rifles. As such, in 1988 it was ordered to produce a shotgun attachment for the rifle, using the same carrying lugs as were already present. The design was finished and accepted for trials in 1990, being accepted for service.
Sometime after the rifle was accepted into military service, it became popular with civilians for use as a sporting rifle. Due to its capability for rapid semi-automatic fire, and its 10 round magazine already existing, making it easier to get past regulations in many regions.
At an unknown date in the 2010s, a Californian man was able to get his hands on a DM35 flamethrower attachment for a G5, since due to regulations a flamethrower is a tool, and attach it to his G5, the rifle having been made compliant to California laws by the attachment of a "Bullet Button". Due to him coming into possession of the Rifle before 2018, it has remained legal to this day, and the man keeps it on display.