Why Swede Momsen would not transform British submarines in 1933

Would sending Swede Momsen to Britain as a naval attaché in 1933 change the Royal Navy submarine force?

Probably not; his diplomatic role and the absence of a formal alliance would sharply limit technical intervention and information sharing.

The counterfactual sends American submariner Swede Momsen to Britain as a naval attaché in 1933. This would probably not materially alter the Royal Navy's submarine force because attachés do not normally direct another service's development. Momsen might discuss rescue work and ideas associated with his own navy, but he would not be free to distribute sensitive American information. Britain and the United States were friendly at the time, yet friendship was not the same as a formal alliance with unrestricted technical exchange.