Hi DocMartyn,
There are some near-surface sub-surface measurements in ICOADS that came from the World Ocean Database. I think the metadata associated with these from the 1930s and 40s indicates that they were mostly made using Mechanical BathyThermographs (MBTs) and CTDs. There was no mention of submarines and there’s no mention of submarines in the latest version of the WOD documentation that I could see.
Best regards,
John