The VK 1601 (Panzer II Ausf. J) was developed with a similar goal in mind to the VK 1801, giving significant up-armoring to the Panzer II concept - 80mm front armor, but similarly found itself under-powered and with middling top speed. Less than thirty were built, and they never saw action.
Portrait of German soldier Rolf Helmudt, taken as a POW and recovering from injuries received during the Battle of Moscow, in a Russian hospital. Moscow Oblast, Russia, Soviet Union. November 1941.
Testing of the Schwimmpanzer II, essentially a water-proofed Panzer II with immense floats attached to either side. The exhausts were protected by the metal contraption on the rear of the tank, and the turret remained free of obstruction so it could fire while still in the water. Development ceased with the cancellation of Operation Sea Lion.
Germany was the leader of helicopter design in the early days, with its Focke-Wulf Fw 61 considered the first really successful, practical design, in 1936. Continuing the trend, the Flettner Fl 265 was perhaps the most advanced helicopter design in the world when it debuted in 1939, pioneering the ability to transition between powered rotary-wing and auto-rotation. Only six were made however as the improved Fl 282 design was favored. It would enter production, with two dozen constructed, and see use as a spotting aircraft and for recon duties.