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Almost certainly coiled, where "coiled" might be using the earth itself as half of a capacitor:

https://en.m.wikipedia.org/wiki/Jim_Creek_Naval_Radio_Statio...

There's at least one other US Navy VLF station as well in Cutler Maine. A few countries have lower frequency ELF transmitters, but the US abandoned its facility.

The sub comms are at 25 kHz, which is 3000m at 1/4 wavelength. So 2 miles makes sense for a 1/4 wave monopole with the Earth as a counterpoise.

The VLF land stations are on 24.8 kHz, which is 7.4miles wavelength. The two mile antenna is probably a 1/4 wave dipole.