Just to add, the Britannia 737's used to swop around frequently (seemed like every other flight!) as well while operating 3 rotations a day - unlike Thomson 737's today (at NCL at least) which stay based for months.
Dan air on the other hand based a 737 at NCL (usually G-BLDE which never swapped) which also worked its socks off but only did 2 flights (as far as I can remember) on a Thursday and no night flight presumably for maintenance/catch up if one of the massive delays quite common in the 80's had struck earlier in the week.