How many letters does the top answer for “installation from which a military force initiates operations” have?

The most common answer is base (4 letters).

Crossword clue: installation from which a military force initiates operations

1 answer found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

base 4 letters wn-def

use as a basis for; found on