An E-3 successor makes a 1981 Shackleton retirement plausible

Is 1981 a realistic retirement date for Shackleton AEW aircraft if Britain fields an E-3-like aircraft in the 1970s?

Yes; a 1970s successor with roughly five years of overlap could plausibly replace the Shackletons by 1981.

Retirement around 1981 is plausible if Britain introduces an E-3-like successor in the 1970s. A period of overlap would allow the old and new airborne-early-warning aircraft to serve together. The suggested overlap is roughly five years. The proposed date therefore depends on when a replacement becomes available.