The projected support-carrier program extended beyond Unicorn, but the ships were at different stages of planning. Unicorn was ordered in April 1939. A follow-on was intended for April 1941, with another potentially following in April 1943 if needed. A third ship had not reached the point of naming decisions. A planned total therefore did not mean that every ship had already been ordered or laid down.
Notable Point · 2:19:02-2:20:06
Why three planned maintenance carriers did not mean three orders
Unicorn's proposed sisters belonged to later financial years, with the last ship conditional on need.