The McDonnell Douglas F-15N Sea Eagle; Tomcat Rival

May 19, 2023

The F-15 is a truly great aircraft. Built from the lessons of air combat over Vietnam, the Eagle was built to be the most capable air superiority aircraft possible at the time. The airframe’s sheer versatility has seen it undergoing continuous updating and modification since it first entered service in 1976, meaning it has expanded from its original design parameters to become not just a formidable fighter, but a first-class strike aircraft as well.

And in the Eagle’s latest iteration, the F-15EX, the aircraft is going to provide the backbone of the USAF for several more decades to come.

Indeed, in terms of the type’s sheer popularity amongst air-heads, I can think of really only one other aircraft that matches it…the F-14 Tomcat.

This epic aircraft, the naval contemporary to the F-15, has a huge fan following, in no small part created by a rather brilliant bit of US Navy propaganda – I mean recruiting – genius.

’ll admit, both these types share a special place in my affections. But just as when you have two great athletes in a sport at the same time, you get rivalry. And though it isn’t remembered so much today, in fact the F-15 at one stage looked like snuffing out the F-14 completely.

Allow me to explain and bear with me because this is essentially the story of two aircraft…actually more like three.

With the F-14 Grumman really did manage to cram the proverbial quart into a pint pot – even if the Tomcat was a pretty big pint pot. Designed to be the ultimate naval interceptor and escort fighter, the F-14 originated from the failure of the F-111B and the TFX program, which had sought to create one basic type to fulfil such diverse roles as long-range intruder for the USAF and interceptor for the Navy.

The F-111B was a costly fiasco, but important lessons were learnt and the Navy, who had been extremely dubious about the whole concept anyway, were able to turn to Grumman to apply those lessons to build them the aircraft they truly wanted. Beginning development in 1966 when it became apparent the F-111B was in trouble, the F-14 was selected to be the Navy’s new fighter/interceptor in 1969.

It was a remarkably ambitious design. The Tomcat employed the most powerful and advanced sensors and weaponry available with a two-man crew to optimize efficiency in long over-water missions. But it also managed to combine this with a surprisingly agile dogfight performance that outmatched just about anything before it and could, in the right circumstance, match that of the new F-15 Eagle that was in advanced development at the same time for the USAF.

I know that’s a contentious statement, no doubt people are typing furiously, but don’t take my word for it. There is a really interesting lecture given by Mike Ciminera, one of the principal designers of the F-14, and he talks about the agility of the F-14 design and its development.

But to get back to the point at hand, all this sheer capability naturally came at a financial cost and as Ciminera put it:

“In those days you paid for aircraft by the pound.”

And that proved so with the Tomcat. The F-14 was expensive, considerably more so than the F-15 Eagle. And as part of the efforts to save on those costs Grumman sought to utilize two of the elements developed for the failed F-111B. After all, $400 million had been spent on the so-called “Sea-Pig” by the time it was cancelled in 1968, and that was far too huge an amount to simply be completely written off.

The first thing carried over was the AWG-9 radar and fire control system, which was fine because it was set up to work with the Phoenix missile. Indeed, the ability to use this missile was a principal requirement for the new fighter as the US Navy was increasingly concerned about the large numbers of advanced long-range Soviet bombers coming into service and, more especially, the high-Mach capable anti-ship missiles they used, and which had been expressly designed and built with countering the US Navy’s carrier taskforces.

But Grumman also used the TF30 engine and this, alas, was a problem. In fact, Grumman and the Navy both knew that this engine was creating issues even during development of the F-111B and with the F-14 the initial plans were for Grumman to produce a limited run of less than sixty F-14A’s which used the TF30, then switch production to the F-14B which would use much improved Pratt & Whitney F401 engines. But in 1971 costs had become a serious issue, and it was spelled out that the F-14 would have to use the TF30 for the foreseeable future.

And this caused concern at the Pentagon. The TF30 was a powerful engine, but it had some vicious stalling tendencies, as well as problems with fan blades coming apart and the powers that be, though enthusiastic by the prospects offered by the new Tomcat as it began flight testing, were wary. After all, they had had one high profile and hugely expensive interceptor project collapse, what happened if another one was to go the same way?

And naturally, as big defence contractors love the opportunity to steal lucrative contracts from their rivals, McDonnell Douglas was swift to swoop in with a potential alternative.

The F-15N Sea Eagle.

This was a comparatively straight forward navilisation of the F-15A, which hadn’t yet flown by that point but was in a state of extremely advanced development. Additional features that would be added to a naval F-15 were folding wing tips to allow the Sea Eagle to stow more efficiently onboard carriers, plus a much stronger tail hook. The F-15A did already have a hook for cutting down landing runs on airbases, but it was recognized that the difference in strain from landing on a deck was much greater, requiring also a beefed up undercarriage.

But to minimize complexity the F-15N would use the same AN/APG-63 radar as its land-based kin, as well as the standard weapon fit of four Sparrow and four Sidewinder missiles, along with the integral 20mm Vulcan cannon. Indeed, the models that McDonnell Douglas put together for their proposal showed the aircraft also carrying Harpoon anti-ship missiles, which considering that was itself only in the design phase shows an interesting forward thinking by the Eagle designers.

This aircraft would ironically provide the commonality that had been the goal of the TFX project that had created the F-111 and looked to be a much cheaper option. And those savings could have been substantial. According to author Bertie Simmonds[i], the F-14A cost $38 million, while the F-15A came in at $28 million each. Even accounting for extra expense for that would be necessary to build the F-15N for service use because of the additional complications in its design and additional development work required, it still would have come in cheaper than the F-14, plus additional savings in the total production costs of the F-15 by all users would likely have been made due to the extra numbers being constructed had the Sea Eagle been selected.

But though these savings would have been welcomed, and to be frank the F-15N likely would have made a fine carrier fighter, it still lacked a critical aspect that the US Navy really, really wanted; compatibility with the AIM-54 Phoenix missile.

The Navy had its sights firmly pinned on this weapon, which was the most formidable air-to-air missile on the planet and considered it key to defeating the threat of long-range Soviet bombers and their lethal missiles. The proposed F-15N was only armed the same as the F-4 Phantom it was intended to replace, and though it was a far more formidable aircraft, the Navy wanted the Phoenix.

So, McDonnell Douglas came up with the F-15N-PHX, which was planned to be able to carry four of the lethal new missiles, though notably the model they made carried six AIM-54s along with a couple of Sidewinders.

I’m going to put that down to optimistic marketing because the Phoenix is both huge and heavy, and even the Tomcat, which was expressly designed to be able to carry six of these monsters, very rarely did so and apparently could only land safely on a carrier with minimum fuel if carrying this loadout.

For fire control both McDonnell Douglas and Hughes stated that they believed the AN/APG-63 could be configured to be compatible with the AIM-54, but consideration was given to fitting the AWG-9 in the Sea Eagle’s nose. However, the estimates were that the F-15-PHX would have weighed an estimated 4,090 kgs (9,000lbs) more than the baseline F-15A, a substantial increase which would no doubt have impacted performance.

But the idea was promising enough that the Sea Eagle concept received consideration up to the highest levels. In 1973 a Senate subcommittee convened to consider in which direction the US Navy should go with their new fighter. This led to one member, Senator Thomas Eagleton, suggesting some Sea Eagle’s be built and a fly off between them and the F-14A been arranged to decide the matter.

But that was not to be, and the F-15N Sea Eagle was to remain essentially a design study and proposal only. The Navy was very much of the opinion that the F-14 was the right aircraft for them, almost certainly correctly as it was built very much to their requirements and not a hash up of an aircraft originally built for the Air Force, an idea that the F-111 saga had firmly soured them on.

So it was that they went with the Tomcat, while the USAF got their Eagle’s. But the whole matter does lead to some interesting points of speculation. “What-if” history is a nebulous thing, indeed it isn’t history, it’s fiction, but it is interesting to consider what might have happened had the F-15N been adopted.

Would it have been as good in the role of fleet defence as the F-14?

Probably not, though it wouldn’t have suffered from the engine issues that bedevilled the F-14A for a third of its service life. Plus, it might well have meant that the F-18 would have proven unnecessary, and maybe navalized versions of the F-15E Strike Eagle would have replaced the A-6 Intruder in service, meaning US carrier air wings had basically a single aircraft design on deck.

It also would mean that the F-15 would likely, unlike their Tomcat brethren, still be the principal aircraft employed by the US Navy today.

As said, all complete speculation, but it does make the McDonnel Douglas F-15N a very interesting “what-if” aircraft.

Note: If you want to know more, I recommend “F-15 Eagle” by Bertie Simmonds. The book’s publisher, Mortons Books, is offering a ten percent discount on purchases to viewers of this channel.

Go to their website and use the discount code EDNASH10 when you purchase. That code is good until the 31st of December 2023, and you can use it multiple times if you want to.

 

Sources/Related:

Mike Ciminera Lecture

https://tacairnet.com/2015/04/15/f-15n-sea-eagle/

https://hushkit.net/2019/03/20/rare-eagles-unusual-f-15s-variants/

https://www.sandboxx.us/blog/sea-eagle-americas-plan-to-put-the-f-15-on-aircraft-carriers/

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[i] Simmonds, Bertie; F-15 Eagle; Undefeated 4th-Generation Super-Fighter; Tempest Books (2021)

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