#t-45d

T-45d male armor.

T-45 Power Armor Suit from Fallout 4 model toy.

The original power armors were developed by West Tek, a major government defense contractor. The West Tek research facility was relocated to Mariposa one year before the war went nuclear. Funnily enough, the MF cells that were developed for the T-51 would have solved the energy crisis that had led to war in the first place …

The Brotherhood is descended from a US military security detachment responsible for security at Mariposa that deserted very shorly before nuclear escalation. It’s not hard to see why they’d have the tech. Outside of FO4 they’ve only been reusing the T-45b and T-51b (sometimes modified and/or - in the case of the T-45, retrofitted for MF cells as opposed to ECs). Since both were standard-issue US military armor, I’d guess there must be a lot of them lying around - both for use and replacement parts.

The Enclave is descended from of a hawkish pre-war faction within the higher US echelons whose members took refuge in fortified or remote locations before the nuclear firestorm. Obviously they’d have the tech. Unlike the Brotherhood they were able to put improved power armor models into service post-war, the advanced power armors Mk I and Mk II as well as the Hellfire armor. (Again including variants, notably the Mk II Tesla armor.) They’re issued to all Enclave foot soldiers so there must be a sizeable number of them. They should also be rather easy to scavenge for someone who knows where to look considering the diverse hits the Enclave has suffered at the hands of … uh, us.

In short, the Enclave has the tech and the resources, while the Brotherhood certainly has the tech, but not (always) the productive capability. (The NCR salvaged power armors have disabled servos. Arguably the NCR has the material wherewithal, but not the tech.) Keep in mind that both the Enclave’s and the Brotherhood’s capabilities wax and wane; also, that both have offshoots, chapters, splinter groups, etc.

I have a theory that we’re dealing with the midwestern chapter of the BoS in FO4 (because of the airships and their apparent active role in FO4). They’re certainly using T-60s in any case. I also have a theory that the T-60 is a revamped T-45 made from plastic composite materials (like the T-51) rather than heavy steel plating. Reduced weight might come in handy when jumping out of airships … It just looks so very similar to the T-45.

The X-01 is more enigmatic since it’s aesthetically quite clearly based on the Enclave’s advanced PA Mk I - yet the different nomenclature suggests an independent line of research. Of course, technically speaking anyone with the know-how and the production capacity could reverse engineer some scavenged power armor and name the resulting product any way they chose.

We just don’t know a lot about the Commonwealth. However, the Institute in particular is obviously a high tech faction with clear pre-war history, like the BoS and the Enclave.

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If none of that answers your question, try here. Come to think of it, I’d love to see an actual factory or large-scale maintenance facility in-game.Thanks for the question though, I really had no idea what to post today ;)

T-45d: A stopgap measure initially developed to stall the Chinese offensive on the Alaskan Front that became the workhorse of the American military in the Sino-American War.