GE used a common body for the various U-boats, so this list is based on phases of the U30B.

All Phase I were built with oil bath air filters. Phase II with the forward radiator intake mounted high had oil bath filters; low-mounted intake was for paper air filters.

Phase Ia- late U28C carbody; radiators slightly wider than the hood, raised section centered between radiator halves, radiator intakes same width as the radiator itself, built-up pilots, small stepwell notch for the handrail, large battery box covers, circular door latches, rectangular headlight casing, tall tapered exhaust stack, large brakewheel.

Phase Ib- same as Phase Ia except radiator intake is shorter, two small intakes appear ahead of the main one.

Phase Ic- same as Phase Ib except the exhaust stack becomes shorter.

Phase IIa- entire hood below the radiator is the same width as the radiator itself, radiator intakes are redesigned, the raised section on the radiator disappears, a horizontal drip rail appears on the sides of the radiator, short exhaust stack, small taper just ahead of the radiator, pipe chain guards at right front corner.

Phase IIb- the taper just ahead of the radiator disappears, six equipment doors on the left side instead of eight.

Phase IIc- the intake screens become corrugated instead of flat, and project slightly from the hood instead of being flush-mounted.

Phase IId- horizontal drip rail on the radiator disappears.

Phase IIe- built-up area on pilots disappears.

Phase IIf1- handrail notch in the stepwells becomes full length.
Phase IIf2- square door latches.

Phase IIg1- headlight casing becomes oval-shaped, not rectangular; cab side drip rail disappears.
Phase IIg2- square door latches.

Phase IIh1- square door laches become standard, battery box covers become smaller, cab door stiffener appears.
Phase IIh2- separate front headlight casing, hinges on front numberboards appear.