German submarine building at Kiel, Germany in March 1937

American naval attaché at Berlin, Germany reported on 30 March 1937 that he recently passed the waterfront of the Krupp Germaniawerft at Kiel, Germany. He sighted six new identical submarines on the ways, probably 500 tons although possible 750 tons. Two submarines were on each of No. 1, 2 and 3 glassed in ways. The building seeed to be a quantity production process.

Source

National Archives USA. Record Group 38: Records of the Office of the Chief of Naval Operations. Series: Secret Naval Attaches Reports. Estimate of potential military strength (pt.). Summaries. Reports from London, Paris, Brussels, Rome and Berlin. Roll M975-001.