Well, in terms of electronics, Yllendthyr is kinda putting a focus on them. Precision and small scale stuff is kinda their specialty.
What I forgot to mention that Yllendthyr will be leading in battery and electric motor technology. Given elven physiology you can also bet their gyros are pretty advanced.
Radars will be commonplace as stationary installations but only my largest and more advanced vehicles would have them as part of their equipment.
As for subs, they exist but the elves didn't realize their true potential.
They are small, their torpedoes are limited and short ranged and generally these are better for scouting than sinking battleships.
In retrospect though Yllendthyr has all means to make a deadly submarine force later. It just won't happen for a while.