A long-range fighter version, the Blenheim Mk IF, was also developed. For this role, about 200 Blenheims were fitted with a gun pack under the fuselage for four Brownings. Later, the Airborne Intercept (AI) Mk III or IV radar was fitted to some aircraft in use as night fighters; these were the first British fighters to be equipped with radar. The Blenheim had been selected as the first aircraft to be adapted for this role as its fuselage was sufficiently roomy to accommodate the additional crew member and radar apparatus. Their performance was marginal as a fighter but they served as an interim type pending availability of the more capable Beaufighter derivative. About 60 Mk IVs were also equipped with the gun pack as the Mk IVF and were used by Coastal Command to protect convoys from German long-range bombers.