Airliner COD

Probably the most obscure corner of carrier aviation is COD, Carrier Onboard Delivery. This is exactly what it sounds like, the practice of delivering high-priority cargo, mail and personnel from bases ashore to aircraft carriers. The role originated in the immediate postwar years, and was first carried out by TBM Avengers modified to carry six passengers or cargo in the former bomb bay. But it was soon clear that the limited cargo weight and volume would be a problem for air-delivery of important cargoes like jet engines and nuclear weapons.¹

A C-1 Trader

The Navy ultimately chose to procure the C-1 Trader, a variant of their existing S-2 Tracker ASW aircraft with an enlarged fuselage. Entering service in 1956, the Trader would go on to serve for three decades in the USN, ultimately becoming the last operational piston-engined aircraft to fly from American carriers. But it was slow and limited in range, and, more importantly, it was soon unable to carry the largest jet engines in use by the fleet. The Navy again turned to Grumman to adapt an existing design with a new fuselage, turning the E-2 Hawkeye into the C-2 Greyhound. Ultimately, it would serve for almost 60 years until the growth of jet engines, in particular the F135 for the F-35C, caused the Navy to procure a new COD airplane capable of carrying it. The winner in this case was the CMV-22,² based on the V-22 Osprey beloved of the Marines and loathed by budget analysts.

The Hercules aboard Forrestal

But while only three aircraft have actually served in the COD role since the mid-50s, there have been numerous other proposals, often for larger and longer-ranged aircraft. In 1963, looking for an emergency option that could better the C-1 Trader's range, the Navy carried out tests aboard Forrestal using a barely-modified KC-130F Hercules borrowed from the Marines. A pair of experienced carrier aviators were checked out on the Hercules and sent to conduct the tests about 500 miles out in the Atlantic. They were able to successfully conduct 29 touch-and-go landings, 21 full stop landings and 21 takeoffs, all without the assistance of the carrier's catapults and arresting gear. Famously, one test saw the Hercules stop opposite the ship's island with "Look Ma, No Hook" painted on the side, and it set a record for the heaviest aircraft operated from a carrier that stands to this day. But there were also problems. The biggest is that while it was technically possible, getting the necessary stopping distances required reversing their engines 3-4' off the deck, a maneuver that is generally frowned upon. The second was that the C-130 is a very big airplane by carrier standards, and landed straight down the deck instead of using the angle, which required the deck to be almost entirely clear of other aircraft. Since the days of Langley, the USN has kept a lot of planes on deck, so even landing a C-130 for five minutes would be extremely disruptive to normal operations, and it was way too large to park out of the way if something went wrong or they needed to wait. As a result of all this, despite the success of the tests, the procedure has never been repeated.

A C-2 lands aboard Lincoln

The Navy was still interested in the idea of a COD plane with more range and capacity than the C-2, and conducted a number of studies over the years. Because it was likely to be a small fleet, and the available funds were limited, very few of these were designed from scratch. Some were intended, like the C-2, to share commonality with other carrier aircraft,³ while others were based on whatever sub-C-130 transport was on the drawing board at the time. But the most interesting were a few proposals to use airliners as the basis for COD planes.

A 737-200 in gray with "United" on the side, so it's basically a USN jet

When I first heard this, I assumed it was a joke, or possibly the result of a gross violation of General Order 99. And while much of me still has a hard time believing it's real, and the former airline structures guy is still running around in terror,⁴ the math is just plausible enough to warrant investigation. The first round of proposals came in the early 70s, with a DC-9-10⁵ and a 737 variant of some sort⁶ put forward as candidates. I'm going to focus on the DC-9, as I have a spec sheet for the military version of the DC-9-30 and I don't have anything equivalent for the 737-200Adv.⁷ Both would have been big for carrier operations, but they were significantly smaller than the later members of their family, and just might have squeezed aboard.

A C-9 flies past a carrier, though not to land on it

Now, to be clear, neither would have fit aboard very well, but the biggest problem the C-130 had was its 132' wingspan, while the DC-9-10's was 89' and the 737Adv was about 93'. While this was still significantly wider than anything regularly flown from a carrier (at this point, that was probably the A-3 Skywarrior at 72.5') the extra 40' and the fact that they were planning to use arresting gear and catapults meant that they could slot (probably fairly awkwardly) into the existing flight deck ops instead of having to kick everyone off. Obviously, sticking around might be a problem but COD birds were generally expected to fly aboard, unload, get refueled and then leave again. Of course, other modifications would be required, and McDonnell Douglas planned to fit not only a tailhook, but also a new nosewheel that incorporated catapult fittings and could be extended to give a higher angle of attack for takeoff, an in-flight refueling probe, and strengthened structure to take the loads of carrier operations. Folding wings were even proposed, though don't seem to have been accepted as part of the initial study.

But all of this assumes that it's physically possible to land and take off in the appropriate distances. Sure, you can do it with a C-130, a plane deliberately designed for short-field operations, provided you have enough wind over deck, but these are airliners designed to operate from relatively big runways. They may not chew up tarmac like the first generation of jets, but would they really be small and slow enough to be compatible with the equipment on a carrier?

An F-111B lands on Coral Sea

Let's start by looking at the problem of landing. Per the SAC, for the design mission (10,000 lb of cargo), the C-9B should be landing at around 73,000 lb, with a power-off stall speed of 85 kts. If we assume 40 knots wind-over-deck, then it's going into the arresting gear at something like 45 kts, but it's also going to be landing at a similar weight to the weight the A-3 Skywarrior, the heaviest plane to regularly operate from a carrier, took off. But weight is only half the story. Speed is the other half, and it's here that I found something surprising. Looking through possible comparison aircraft, I found the F-111B, the result of an extremely dumb attempt to turn an Air Force light bomber into a Navy missile-slinger. It was cancelled before entering service, but it was definitely carrier-capable and even flew a few carrier tests. And at the maximum listed landing weight of 57,000 lb, it was stalling at about 100 kts, for a speed relative to the deck of 60 kts. If we assume that the arresting gear is basically limited by the kinetic energy of the landing aircraft⁸ then the total kinetic energy of the F-111B is 102.6⁹ while the C-9B comes in at only 74.1, a value lower enough that I'm actually reasonably confident that this could have worked, structural issues aside.

A Skywarrior prepares to launch, also from Coral Sea

But what about launch? Here, we're going to use the A-3B, the heaviest plane regularly to take off from a carrier,¹⁰ as our exemplar. It took off at 73,000 lb and a power-off stall speed of 124 kts. The C-9B's numbers are a takeoff at 99,700 lb and a power-off stall speed of 100 kts. If we again assume 40 kt wind over deck, we see the A-3 needing to get 257.5 from a combination of its engines and the catapult, while the C-9B needs only 179.5. Weirdly, it looks like the C-9 actually has a slightly higher thrust-to-weight ratio than the A-3, so again, we pass a plausibility check for this scheme.¹¹

An F-28 from a carrier navy on final approach, sadly sans tailhook

Despite the fairly impressive performance (10,000 lb of cargo for 2,200 nm) the plans for the C-9 COD went nowhere. But it was far from the only airliner proposed for conversion, either in the early 70s or later. I've already mentioned the Boeing alternative, but at the same time, Hawker-Siddley proposed a version of their HS 748 turboprop airliner, with folding wings and the usual structural modifications, but it seems to have gone even less far than the jet alternatives. Later, in the 80s, when the Navy was looking at a new COD plane to replace the C-2, they seriously investigated the Fokker F28, a somewhat smaller airliner than the DC-9 and 737, but ultimately decided to build more C-2s instead. And it looks like we'll probably never see such proposals again. Modern airliners are less rugged, because structural weight costs money to haul around, and there's just not much demand for a long-range high-capacity COD, particularly now that the CMV-22 has aerial refueling capability. But it's an interesting rabbit hole of history to go down.