Why is JSOW a Navy only weapon?

If I understand things correctly JSOW has been integrated into F-35C, not A or B, which isn't surprising since USN is the only US service branch that has remained interested in purchasing/deploying JSOW. It was initially popular with USN for SEAD operations since cluster munition nature was quite effective against soft targets, while USAF went with WCMD for their cluster munition of choice.

Given cluster munitions question marks and current variants of JSOW where can penetrate bunkers, receive course updates, hit moving targets with IIR, etc. my question would be why does it remain a one branch weapon? What exactly about JSOW keeps USN interested but USAF wants nothing to do with it?

As has been said before, all F-35 variants (of the same block) share the same software build. It would only take the "flip of a switch" for the A to carry the JSOW. They did not do it for Block 3F as they were trying to get it done as soon as possible but if it came to a wartime need, they could do it if they wanted it to. Block4 with UAI will clean up a lot of the holes in the weapons roadmap.

I find this strange too and it's integrated (or at least tested) with pretty much all fighters or bombers in USAF service (F-16, B-1, B-2, B-52, F-15E). Navy fact file even mentions F-117 and A-10 as platforms for it. Also F-35A is mentioned as platform there. It also seems pretty popular weapon in other countries although not quite like JDAM or SDB. I'd say that USAF thinks that combination of SDB, JDAM and JASSM is good enough and JSOW is redundant to its needs. Bit like US Navy has not bought any JASSM missiles even though it has been integrated with Hornet, Super Hornet and most likely also by F-35s. I think USAF would get JSOW quickly from USN if needed and USN would similarly get JASSM if really needed. The capability to carry and use them seems to be there, although I don't know how much training would be required to use them.

As has been said before, all F-35 variants (of the same block) share the same software build. It would only take the "flip of a switch" for the A to carry the JSOW.

Isn't it hardware testing too though? They flew an F-35C and tested release characteristics of JSOW at various speeds to approve it's ability to physically release the weapon within various flight envelopes.

An F-35A is similar to an F-35C, but in the end they are two different planes with different weights and flight characteristics. Of course we can assume hey it works on an F-35C therefore close enough, but I'm not sure weapons testing works that way across F-35 variants. If they haven't done thorough testing of releasing JSOW test rounds from an F-35A I'd be quite surprised if anyone was willing to just flip a switch since same software.

An F-35A is similar to an F-35C, but in the end they are two different planes with different weights and flight characteristics

They have the same weapon bay, so weapons separation should be the same. Admittedly, F-35 is heavier and can generate more lift, but i don't think they need separate testing for that, kinda like how you don't need to re-test weapons integration when a newer heavier F-16 came out

Same bay, same ejectors, etc. It was a cost/time/need savings measure to cut them from 3F.

I'm skeptical.

I've seen lists of tests completed on F-35 before where they have different dates and qualifications across different variants for same weapon. Like F-35A with GBU-31, then on a different date F-35C with GBU-31, etc. so that leads me to believe they do in fact qualify weapon separations across different variants even if they have the same sized bomb bay. Same with external carriage, they'll show testing with an F-35A, F-35B, and F-35C with Sidewinder off the wing.

Yet I've only seen JSOW separation test completion on F-35C.

While they may & should "qualify" the most weapons separately, that does not take away from the fact that the underlying software is capable of using the weapon prior to qualification.

As I said, it a cost & time issue balanced against need getting to Block 3F.

I'm skeptical.

I've seen lists of tests completed on F-35 before where they have different dates and qualifications across different variants for same weapon. Like F-35A with GBU-31, then on a different date F-35C with GBU-31

A good portion of that was done to validate the CFD/wind-tunnel model predictions that
the CV/CTOL weapons bay trajectory effects were very very similar.

You would see a pretty abbreviated stores separation test (if any) if the Air Force elected to go
for internal carriage of JSOW on the A.

Of course, the Navy hasn't bought JSOW in nearly four years and the line is on life support.
JSOW-ER is interesting and they've got money for a Phase 3 Part B demonstration but
an actual weapon is likely to require a distinct integration effort all its own.

Only thing I can think of is G limitation. Will the Sea variant be able to test, launch envelopes greater than 7.5Gs. Is that even a consideration for employing JSOW. if it is, then the A variant might use the same launch and carriage envelopes as the C.

"remember boys, when carrying JSOWs, you're a 7G airplane".

I really doubt anybody would be launching glide bombs using high-G maneuvers. I doubt even any toss/loft bombing method would generate more than 7.5Gs. Most fighter aircraft are restricted to 4-6 Gs when carrying heavy ordance to begin with.

F-35A is a 9G aircraft with full internal weapons load. I take it that it can maneuver up to 9G when carrying those weapons, but I wonder what the launch envelope limits are to release those internal weapons? I think it's probably lower than maneuvering limits, but I could be totally wrong.

I think since it's totally software controlled aircraft that it probably can limit itself according to weapons carried.

I have little doubt that the A model can pull 9Gs while carrying JSOWs internally, but what about the weapon itself.
Can JSOW survive a 9G pull? will it damage the weapon or something.
Can the A even pull 9Gs without putting some kind of strain to the pylons, specially when mounted externally.

These are questions that can't be answered by the Navy's C model weapons certification test. Not unless the C model has a G override switch like the SHornet and they decide to conduct 9G envelope testing with JSOWs

I have little doubt that the A model can pull 9Gs while carrying JSOWs internally, but what about the weapon itself.
Can JSOW survive a 9G pull? will it damage the weapon or something.
Can the A even pull 9Gs without putting some kind of strain to the pylons, specially when mounted externally.

These are questions that can't be answered by the Navy's C model weapons certification test. Not unless the C model has a G override switch like the SHornet and they decide to conduct 9G envelope testing with JSOWs

The F-35 has no G restrictions, with internal payloads (that includes weapons/pylons.) Delivery envelopes are an entirely different matter.