USRPT for marathon swim training?
USRPT (Ultra Short Race Pace Training) is designed to work for 100 - 1500 m events, and for 1500 m, 24 - 30 reps of 100 m are suggested.
I love the idea of USRPT for fast feedback and specificity, however, is it possible to adapt this training method to longer race distance, e.g. 5 km, 10 km or even 25 km, e.g. offering 1.5 - 2x of race distance using 200 m - 400 m intervals at race speed, with 20 seconds rest each.