PING sound when asking for depth under keel.

[Sailor Steve]

Originally Posted by CptGrayWolf

btw anybody know if type VII U-boats even had this IRL?

Yes they did.

The Echelot Gear

The shallow water gear is of the super-sonic type, using a magneto-striction transmitter of frequency 1,500 cycles per second and a similar receiver unit, mounted horizontally, 28 in. apart, in a flange welded near the bottom of the hull. Transmission is by the condenser discharge method. The deep water gear consists of three "Wall" type sonic transmitters connected in parallel and three moving coil receivers connected in series, mounted in the keel, 32 ft. 6 in. apart.

An alternator giving 1,500 cycles per second, provides the power for the transmitters at the working frequency of 3,000 cycles per second.

The same depth indicator, namely a rotating neon tube, is used for both deep and shallow sets, the ranges being 0-125 metres shallow and 0-1,000 or 0-3,000 metres deep.

Provision is also made for hand transmissions and aural reception, using a stop watch for determining the depth.
http://www.uboatarchive.net/U-570BritishReport.htm

Bottom of page 28.