When the attack on Pearl Harbor brought about the entry of the United States in the Second World War, not one single aircraft was in operational use that was capable of night fighting let alone equipped with an airborne intercept radar. The US military, however, had long been cognizant of the need for a night capability and ten months prior to the attack on Pearl Harbor had already awarded a contract to Northrop for the prototype XP-61A Black Widow night fighters. In the interim, the Douglas A-20 Havoc light twin bomber was modified with British AI (air intercept) Mk. IV radar sets that were built by MIT and an underfuselage pannier that housed four 20-millimeter cannons. This Havoc variant was designated P-70 and the prototype made its first flight in September 1941 before the US entry into the war. It's little known that this interim night fighter conversion did have the name "Nighthawk" but it was rarely used in practice. While most Douglas P-70 Nighthawks remained in the United States to train crews bound for night fighter operations, a small number did serve in the Southwest Pacific where the aircraft was found to be slow and lacking in high altitude performance.
On 26 January 1943, the USAAF activated its first dedicated night fighter squadron, the 414th Night Fighter Squadron, in Florida at Kissimmee Army Air Field with sixteen officers and enlisted personnel transferred in from other units. Three other squadrons (415th, 416th, and 417th NFS) were also established in Florida where the USAAF had its School of Applied Tactics in Orlando. Given the highly technical nature of night fighting by radar, pilots were specially selected for their technical skills and above average flying skills. The radar operators were selected were the first AI (airborne intercept) radar observers to come from a special training program started by the Army Air Forces. At Kissimmee AAF the pilots and radar observers trained together as a team on the Douglas P-70s. After a month of training, the crews of the 414th NFS were sent to the UK for further training with RAF night-fighter crews on Airspeed Oxfords, Bristol Blenheims, and Bristol Beaufighters. With the P-61 Black Widow not expected to be operational in Europe until the end of 1944 to early 1945, a "reverse" Lend-Lease was arranged in which over 100 radar-equipped Bristol Beaufighters were transferred to the USAAF as they were more capable than the underpowered P-70s used in training. The 414th NFS's radar observers found the transition from the American copy of the AI Mk.IV radar set to the British version. Although identical, wartime experience introduced a set of improvements to the British sets on the Beaufighter that the American versions on the stateside P-70s lacked. To give you an idea of the limitations of the airborne radar sets of the day, the British AI Mk.IV was only usable over 15,000 feet due to ground clutter at lower altitudes and had a detection range between 400 feet to only as far out as 3 miles!
Following their respective conversion training, the pilots and radar observers of the 414th NFS reunited at RAF Valley in Wales where they took delivery of twelve Beaufighter Mk.VIFs. With additional training through the early summer of 1943, they were joined by the 415th NFS and the two squadrons of American Beaufighters shipped out to North Africa. The second group of squadrons, the 416th and 417th NFS, followed them in August 1943 to North Africa as well. Leaving the UK in groups of five aircraft and led by a Coastal Command Beaufighter for long-distance navigation. After stopping over in Gibraltar, the Beaufighter squadrons then proceeded to their operational bases in Tunisia and Algeria. Operational necessity, however, had the American crews flying daytime interdiction missions against German and Italian aircraft making supply runs to North Africa across the Mediterranean Sea. On the first combat mission for the American Beaufighters, a Heinkel He 115 floatplane was shot down by aircraft from both the 414th and 415th NFS. By the end of the month, however, wiser heads prevailed that didn't wish to waste the specially-trained night fighter crews on daytime air and shipping interdiction missions. Night time enemy air activity would be quiet for the remainder of 1943 until the Allied landings at Anzio, Italy, on 22 January 1944. With the beach heads only thirty miles from Rome, for the next four months some of the most savage fighting until the Battle of the Bulge took place as the Germans tried to overrun the Allied pocket at Anzio. Luftwaffe bomber units based in southern France increased their night time raids on the landing zones and the American Beaufighter squadrons were moved to an improvised base on the island of Corsica to be better positioned to intercept the nocturnal Luftwaffe raiders.
On 23 January 1944, the day after Allied forces hit the beach at Anzio, 1Lt. James Anderson would of the 414th NFS would score the first night kill for the American Beaufighters against a Dornier Do 217. That first night many of the pilots of the 414th NFS would fly two, even three missions from their improvised base. Of the twelve Beaufighters in the squadron, nine of them flew nearly nonstop that first night. By the time Allied gains at Anzio had been consolidated, the 414th NFS had converted to the vastly improved AI Mk. VIII centimetric radar set. The squadron was then moved to the mainland in October 1944 and two months later converted to the Northrop P-61 Black Widow. The 415th NFS operated from bases in Sicily after moving across the Mediterranean, as did the 416th NFS where they covered the Allied supply line from North Africa to Italy. The 416th eventually got moved forward to Italy itself as well while the 417th stayed behind in North Africa to cover the rear logistics areas of the Allied invasion of Italy before moving to Corsica in 1944. By that time, those three squadrons had also converted to the AI Mk. VIII centimetric radar set for their Beaufighters. In addition to the night fighter patrols, the three squadrons' Beaufighters also flew night intruder missions against ground targets as well throughout Italy during the drive northward from Anzio.
With the Beaufighter squadrons now based on Corsica, they were well-placed to protect the Allied invasion assembly areas for the August 1944 landings in southern France, Operation Anvil-Dragoon. In addition to night fighter patrols of the rear logistics areas on Corsica and the assembly points for the invasion fleet nearby, the squadrons were also tasked with night intruder missions on various Vichy and German targets in southern France in the run up to the 15 August landings between Cannes and Toulon. Once the Allies had captured the port city of Marseilles, the 417th NFS was moved forward to Le Vallon in the Rhone River valley to intercept German reconnaissance flights and raids on Marseilles where incoming Allied forces were being disembarked. Other missions included the continued nocturnal raids and patrols for increasing numbers of midget submarines seeking to disrupt the Allied shipping in Marseilles harbor. By this point the Beaufighters were over three years old and much overhaul work had been delayed due to the combat situation. In less than three months, the 417th NFS alone would lose nine Beaufighters to technical problems. By the end of 1944, the USAAF decided to begin the drawdown of Beaufighter operations- the 414th NFS, still operating in Italy, was the first to convert to the P-61 Black Widow in December. The 415th NFS, operating near Nancy, France, converted to the P-61 Black Widow as well. The 416th NFS traded in its weary Beaufighters for the De Havilland Mosquito NF Mk. XIII and the 417th NFS, the last of the four night fighter squadrons, was moved northward to Belgium and traded in its Beaufighters for the P-61 Black Widow in March 1945, marking the end of the unique "reverse" Lend-Lease operation for the USAAF.
Source: Air Fan International, July 1996, Volume 1, Number 5. "Southern Beaus- USAAF night fighter operations in the Mediterranean during World War II" by Rene J. Francillon, p54-63.