Just to be thorough and make the point:
Can an attacking submarine immediately submerge before combat begins considering there is no enemy destroyer like in A&A Europe?
To prevent opposing transport from loading/offloading.
No. In AARevised (unlike AAEurope and AAPacific) an attacking sub must survive one round of combat first and can only submerge if there is no defending DD present. In other words, there is no “substalling” in AARevised.
Thank you SS.