Yes, except south of Saigon, the former MR4 (IV Corps) was mostly swamps (the Mekong Delta).

Officially called Military Regions I, II, III, and IV; aka I Corps, II Corps, III Corps, and IV Corps. I Corps was near the DMZ, II Corps was the Highlands, III Corps Saigon AO (Area of Operations), and IV Corps was the Mekong Delta.

It's not - the Russians have always had lower profile sails on their boats compared to Western boats. The Borei is a successor to the Delta-class submarine; the sail seems a bit longer, but the height is about the same as a Delta-IV.

From the Mekong Delta (IV Corps) to the DMZ (I Corps); from the China Sea to the borders of Laos & Cambodia. RVN was blanketed with GIs.

The motto of Delta Delta Delta is 'love one another'.