[twawaaay]

Exactly.

During WWII the already had radars enough to detect periscopes sticking out of sea surface from tens of miles.

They were also able to triangulate subs by their short transmits anywhere on the Atlantic with pinpoint precision.

People very much underestimate technical military capabilities.

The issues with militaries are of a different kind -- sifting through deluge of information, prioritising, making right inferences, etc., not the ability to spot and triangulate the enemy.

[orangepurple]

I think periscope detection is only possible since the 1970s

  The opportunity to detect periscopes was exploited in early radar experiments that prompted the development of the AN/APS-116 radar manufactured by Texas Instruments in the 1970s. The AN/APS-116 is an Xband, high-resolution, fast scanning system developed specifically to provide a periscope detection capability on the carrier-based S-3 aircraft. The AN/APS-137 is an upgrade of this radar used primarily on the S-3; a limited number are also used on the land-based P-3 aircraft.

https://www.jhuapl.edu/Content/techdigest/pdf/V18-N01/18-01-...

[petre]

It has been possible since WWII, only not from tens of miles:

"During the early months of the Battle of the Atlantic in World War II, British ships using the radar set Model 271 were able to detect the periscope of a submerged submarine at a distance of 800 m (0.50 mi) during tests in 1940."

https://en.m.wikipedia.org/wiki/Submarine_snorkel