Lightning round!

T-45 was the first production model of Power armor given to the US military... T-45D technically. cool. It was the base line heavy model. Powered by a single micro fusion cell.

T-51 was the refinement of the T-45 model. It was loaded with a TX-28 MF Pack Generator that would pump out 60,000Watts of power for the suit and would last over 100 years if in constant use.
Made of the latest poly-laminate composite, the T-51B model's shell is lightweight and capable of absorbing over 2500 Joules of kinetic impact. The 10 micron silver ablative coating can reflect laser and radiation emissions without damage to the composite subsurface.

T-60 the oddball.
Developed in early 2077 after the Anchorage Reclamation, the T-60 series of power armor was designed to eventually replace the T-51 as the pinnacle of powered armor technolo-

... no. that explanation that Bethesda gives is crap. Lets go into what the fans at NMA (No Mutants Allowed) have to say...

T-60A, was an advancment of the T-45 power armor to focus on CBRN and cheap home land security armor. taking the supperior servos and tech inside the T-51B, throwing it under the hood of the T-45D, then making the T-60 airtight with atleast 4 hours of reserved air, ontop of the standard intake filtration system. Thicker joints made of activated carbon and boron fused with rubber protects the wearer from radiation and biological surface damage.
It bacame a great fill in for an armored CBRN home land protection suit of armor that was cheaper to make than a combat focused suit of power armor.
... Powered by a single MF core to save space on the back for the x2 oxygen tanks.