Grumman’s entry into the “heavy fighter” sweepstakes was destined to never advance beyond the prototype stage. But its not an easy thing to dismiss it as a failed design.

Let’s take a look at an interesting design; in particular WHY it wasn’t built and if it plausibly COULD have been.

The United States’ aircraft industry of World War II was massive. That is an understatement. In 1944 the US outproduced the combined Axis by about 2.5:1 in aircraft engines. But resources were not infinite and many choices had to be made. Much of that was handled by the War Production Board (WPB), a powerful bureaucracy established by President Roosevelt in January 1942.
It is mildly surprising such a thing could exist in a country founded on ideals of free enterprise and free markets. But all through the War years, until the board was dissolved in November 1945, nothing could be made without the Board’s stamp of approval. With a dozen field offices throughout the country they determined what was made by whom, and what priority everything got for resources, factory space and labor.

Of course the downside to such oversight is the difficulties of adjusting on the fly. In one interesting instance a change in priorities led to some high level bargaining. Before the War, the US Navy had been looking for a next generation of long range patrol sea plane. The PBY Catalina was very long ranged, but slow and not a very heavy lifter. A next generation was in development that would also see Wartime use; Consolidated’s PB2Y Coronado with twice the Catalina’s power (4 x R-1830 engines) as did Martin’s PBM Mariner with two R-2600 engines.
So maybe I should say they were looking for the next, next generation.
Boeing had submitted a very powerful and capable twin engine design. The PBB Sea Ranger used two R-3350 engines, that’s the same engine developed for the B-29. It was bigger and faster than its predecessors, and had more than twice the range (over 6000 miles). It is still considered one of the largest twin, piston engine aircraft ever built. The Navy was very excited about the design’s potential and had ordered a prototype before the War. It first flew on July 5, 1942 and the WPB allocated a whole new factory in the Seattle area (Renton) to build it.
Within a few weeks the Navy decided it would be way too late in coming. They needed long range patrol planes, that could carry a significant load now, not in two years. They especially were worried about the mid-Atlantic where no planes could patrol and U-Boats were sinking Allied shipping at a frightening pace.
So the Navy called a meeting with the Army Air Force and the War Production Board. They wanted B-24 Liberators and B-25 Mitchells, and they were willing to trade one Boeing factory in Seattle to get them. This is one of the best examples of adapting to changing circumstances (by a bureaucracy!) I know of. The Navy got a large allotment of long range patrol bombers (as the PB4Y Liberator) and an excellent medium bomber for the Marines (as the PBJ Mitchell) while the Army Air Force got a fourth major factory for the B-29.

This story makes me think of the F5F and how it could have wound up being built.
There were a number of bottlenecks and shortfalls in manufacturing. What if, for some reason, there was a shortage of R-2800 engines? This could be anything from inadequate or slow expansion of necessary plants, to a prolonged labor dispute (yes, there were some of those in the US!), to a really unfortunate fire or natural disaster. Seriously, there were three important fighters (P-47 Thunderbolt, F4U Corsair and F6F Hellcat); one medium bomber (B-26 Marauder), one transport (C-46 Commando), a night fighter (P-61 Black Widow) and a number of lesser types all tied into that one powerplant. Even if only one key factory was affected it could have lead to a shuffling of priorities.
I can imagine the Army Air Force taking this to the WPB for relief. “We need Thunderbolts and there aren’t enough R-2800s to go around!” Under extreme pressure the Navy may decide they could accept 1500 F5F Skyrockets and delay the F6F Hellcat’s entry to service. This might mean the AAF would have to sacrifice some R-1820 engines, less production on B-17 and C-47 perhaps? Or maybe Wright could just make up for Pratt and Whitney’s shortfall? If they had the capacity I have no doubt they’d be happy to make the engines!

Could the Skyrocket ever have been considered as an acceptable “modern” fighter? Certainly Grumman saw it as a next-gen offering to replace the Wildcat. The F6F Hellcat had 2000 horsepower and a take-off weight of 12500 lbs. The F5F had 2400 horsepower and a take-off weight of 10000 lbs. The F6F posted a top speed of 386 mph, the F5F 383 mph.
So maybe the more interesting question becomes, why wasn’t it built in the first place?
There were stability concerns, and the one prototype received numerous tweaks and two major rebuilds that were largely focused on yaw stability. But most test pilots were actually pretty enthusiastic about its potential and downplayed those stability concerns. In fact, I’ve seen it stated that a lot of those changes were more about aerodynamic data collecting for the later F7F Tigercat than actually fixing anything wrong with the Skyrocket. [keeping in mind, there actually was no R-2800 shortage and the new engine was performing brilliantly in all development tests. It was decided before the XF5F prototype ever flew that it was a test aircraft and not a new production type].
The best explanation I’ve seen for the “no build” decision is just that it was more “expensive” to build, maintain and support than the new F6F would be. The F5F would burn more fuel and needed more parts inventory, thereby reducing the number and frequency of airstrikes a fleet carrier could launch before it needed to resupply. American industry was certainly up to the challenge of meeting demand, but the carriers would be more closely tied to their supply ships.
So if the F5F had been built, fleet carrier operations would have likely been slightly less aggressive for the year from late 1943 until late 1944 when the F6F-5 finally took it’s place. Although my guess is the difference would actually be quite small.

So what about this fine “operational” Skyrocket I’ve built? The kit is by Minicraft, they actually did two XF5F-1 kits; one of the original prototype and another for after its first major rebuild. Both kits have a number of alternate parts so you can build the plane in several different iterations from its testing. The second rebuild was clearly more about the F7F (tricycle landing gear and a lower canopy with less framing) so its of less interest to me anyway. I chose the kit of the original build of the aircraft, but with the tweaks that were quickly applied (a fillet at the fuselage/wing join to smooth airflow there and enlarged rudders to improve yaw control) with the reasoning those tweaks were probably most about making the actual F5F as good as it could be.
My guess is the Skyrocket’s performance would be completely adequate. Although with a very limited production run it might have only operated from the big fleet carriers, while the Independence class light carriers got FM-2s (hot rod Wildcats). The central Pacific campaign through the capture of the Marianas would have occurred with few changes from actual history. By the start of the Philippines campaign in October 1944 the F6F-5 would have replaced the F5F-1 in all but a couple of squadrons. But the Philippines campaign also means the start of Kamikaze operations. Suddenly a fighter that can climb to altitude like, well, a skyrocket, seems like a pretty good idea! And those last couple squadrons remained in service as long as parts held out for them.
This plane is in the markings of a Fighting 19 Hellcat flown by Bruce Williams, shown here with 7 kills. I’m willing to guess Bruce Williams could have still scored 7 kills in a Skyrocket. the decals are by Techmod.