CREATE TABLE table_204_161 (id DECIMAL, "name" TEXT, "1968 cf\ designator" TEXT, "place of\ manufacture" TEXT, "primary\ role ( s ) " TEXT, "service\ period" TEXT, "#\ used" DECIMAL)

how many airco dh .4 's did the uk use in their period of service ?
SELECT "#\nused" FROM table_204_161 WHERE "name" = 'airco dh.4'
SELECT "#\nused" FROM "table_204_161" WHERE "name" = 'airco dh.4'