Germany would consider to arm her battleships with a maximum caliber of 38cm/14” guns according to a memorandum of US secretary of the Swanson dated 10 April 1937

Anchored in the Alta Fjord, Norway between 1943-1944.

 U.S. Naval History and Heritage Command, MH 71390

In a memorandum for president Roosevelt wrote secretary of the Navy Swanson (1)on 10 April 1937 regarding the caliber of the main guns for new battleships that Germany was willing to accept a maximum caliber of 38cm/14” if other naval powers did the same. However if an exception was made for the Soviet Union for her first two battleships, Germany retained the right to arm her future battleships with a aximum caliber of 40.6cm/16”.  

Notes

1. Claude Augustus Swanson (31-3-1862 Swansonville, Virginia, USA-7 July 1939 Rapidan Camp, Virginia, USA) secretary of the Navy 5 March 1933-7 July 1939.

2. The Bismarck-class consisting of the Bismarck and the Tirpitz had a main armament of4x2-38cm15”C/34 guns. The preceding Scharnhorst-class 3x3-28cm/11” C/34 guns, the planned but not realized H-class was heavier armed varying betwen 40.6cm/16.0” and even 5-0.8cm/20.0”.  

Source

Franklin Roosevelt D. Roosevelt Presidential Libray&Museum. Map Navy Department October 1936-1937 FDR’s President’s Secretary’s File (psfc000057).