By Tommy H. Thomason

Friday, March 13, 2020

U.S. Navy 1950s Light-Attack Jet Programs

By January 1952, nuclear weapons light enough to be carried by tactical fighters and bombers had been qualified and were being stockpiled.
The Mk 7 was an implosion-type device, which meant it was relatively large in diameter. The Mk 8 was a gun-type device, smaller but much heavier, of interest to the Navy because it could withstand the shock of hitting the ground or water at a high incidence angle and speed, making it effective against submarine pens and ships/submarines. The subsequent improvements were the Mk 11, replacing the Mk 8, and the Mk 12, which was notably lighter and smaller than the Mk 7.

The Navy's carrier-based candidates for the new bombs were the Douglas AD-4B Skyraider and the McDonnell F2H-2B Banshee, with the B suffix standing for the armament changes necessary to carry, arm, and drop the Mk 7 and Mk 8. While modifications to Skyraider were relatively minimal, the -2B required a larger strengthened pylon, inflight refueling capability, and landing gear modifications to increase the ground clearance in order to taxi and takeoff with the Mk 7 even with a retractable fin.

F2H-2B side numbers 103 and 107 have inflight refueling probes and the requisite pylon under the inboard section of the left wing.

The AD-6 did not require a B suffix because it came off the production line with the nuclear-strike capability.
Although white in gray-scale photos usually indicate florescent paint, it's possible that in the photo above it is in fact white paint in order to minimize the effect of the temperature spike from the bomb's detonation on the thinner skins of the control surfaces.

The AD had excellent range (a combat radius of almost 900 nautical miles) but a cruise speed of only 163 knots, which means a maximum range mission required 13 hours or more in the saddle. The F2H-2B had equivalent range with inflight refueling and a cruise speed more than twice that, 411 knots. The other shortcoming of the Skyraider was that it could only accelerate to a speed of 270 knots on the run-in to the target and for egress, which meant that being hoist by its own petard was a real possibility. The Banshee, even with its straight wing, could reach 500 knots, which means it could throw the bomb farther and be miles more away when it detonated.

While the Navy continued to assign the Skyraider to prospective nuclear-strike missions, it was clear that jets were to be preferred. The Bureau of Aeronautics (BuAer) considered several options, deploying five different ones in the 1950s in addition to the F2H-2B.
The McDonnell F2H-3/4 benefited from the -2B experience and all were delivered as nuclear-delivery capable so the B suffix was not required.
Note that the Mk 7 tail cone is rotated slightly counter-clockwise and the landing gear struts are pressurized to provide minimal ground and airframe clearance during taxi and launch.

In the meantime, the Navy's Bureau of Aeronautics contracted with Douglas, sole source, for the diminutive A4D-1 Skyhawk, a bespoke design optimized for the Mk 7-delivery mission. This early A4D-1 has a VHF navigation pod in place of the Mk 7 that dictated the long landing gear.

The F7U-3 was qualified to deliver nuclear weapons and deployed with several VF and VA squadrons. In parallel with the A4D program, the Navy contracted with Vought for an attack derivative of the Cutlass, the A2U.
However, the A2U-1 was cancelled based on the development problems with the Westinghouse J46 engine and the availability of another, less expensive option from North American, the FJ-4B.

The transonic FJ-4 had been procured as a day fighter but the supersonic Vought F8U Crusader resulted in it being delivered exclusively to Marine Corps fighter squadrons. However, it was well thought of and therefore an ideal candidate for the strike mission when modified with extra stores stations, controls for the nuclear weapon, and an additional pair of speed brakes. The result was the FJ-4B.

In the above display, a Mk 7 was loaded on the left pylon outboard of the refueling probe.

To fill the need for jets in attack squadrons before the A4D-1 and FJ-4B became available, BuAer procured the swept-wing F9F-8 Cougar as the F9F-8B beginning in 1954. This was possible at that point because the smaller Mk 12 was now qualified and provided adequate ground clearance with all four of its fins folded.


Nevertheless, none of the Navy's single engine nuclear-strike airplanes then available were all-weather capable. The Douglas F3D-2 night fighter was evaluated to fulfill that requirement but proved inadequate for other reasons.

Although the McDonnell F3H Demon, like the F7U-3, was intended to be a general purpose fighter with nuclear-strike capability, it doesn't appear to have been operationally assigned that role.

In early 1954, North American Aviation submitted an unsolicited proposal to BuAer for its NAGPAW, a single-seat, transonic airplane powered by two afterburning J46 engines that addressed the all-weather capability shortfall. The North American General Purpose Attack Weapon incorporated one of the first inertial navigation systems, an early stealth feature because it emitted no electronic signal betraying the airplane's presence (it was equipped with a small radar that could be used briefly and intermittently to update its position with respect to radar-significant ground features). Another unique design concept was the linear bomb bay. Conventional bomb bays eliminated the drag of the stores but were sometimes reluctant to allow the stores to drop out on release due to turbulence within the cavity. The linear bomb bay allowed the bomb to be positively expelled out the rear of the airplane along with empty fuel tanks.
The BuAer was interested but added requirements, e.g. a second crewman, zero wind-over-deck launch, and Mach 2 performance. The eventual result was the much bigger and faster A3J Vigilante. For more on NAGPAW, see https://tailhooktopics.blogspot.com/2020/03/north-american-general-purpose-attack.html

By the early 1960s all of the Navy's light-attack jets except for the A4D Skyhawk had been retired. Already the lowest cost, both procurement and operating, of the alternatives, it had been upgraded early during its long production run to include an all-weather capability. For more, see the revised edition of my book on the Scooter, published by Crecy and also available from Amazon: http://www.crecy.co.uk/scooter-the-douglas-a-4-skyhawk-story