Here are some photos I took of these German Focke-Achgelis Fa 330 Bachstelze (wagtail/sandpiper) at the NMoUSAF and Udvar-Hazy.
These could be towed behind submarines to locate targets more than 30 miles away. The pilot could telephone down what he could see from a height up to 722 feet. A crew of four could assemble or disassemble the Fa 330 in three minutes.