Sébastien Roblin for The National Interest in a piece called Germany Does Not Have One Working Submarine:

One unfortunate consequence is that the submarine crews are completely unable to gain badly needed operational experience. Only by mid-2018 will three German submarines be operational, followed by possibly a fourth that November.

But the kicker is that the Deutsche Marine would not be able to deploy its full submarine force even if all six were in operational condition. According to Bartels, there are only three trained crews available to man the six Type 212As.

Indeed, the German military, which transitioned to being a purely volunteer force in 2011, has struggled to fill its ranks […]

Low readiness rates afflict other branches of the Germany military as well. For example, Germany is currently expanding and upgrading its fleet of Leopard 2 tanks. However, according to NTV, out of 244 Leopard 2 tanks already in service, only ninety-six are combat-ready, while eighty-nine are awaiting spare parts, seven are devoted to R&D and fifty-three are under maintenance or receiving upgrades. Of fourteen new A400M transport planes, sometimes none are in operational condition; one broke down in February 2017 while transporting Defense Minister Ursula von der Leyen. In 2015, it was revealed that out of ninety-three Tornado strike jets officially in service, only thirty were combat ready.

Meanwhile some are still speculating how Germany could possibly spend 2 percent of GDP on defense.