Yes the submarines are on VLF, but it is the land based stations that use the massive antennas, but even these are only a fraction of a wavelength. The reason VLF is used is because a submarine does not need to surface to receive it as VLF penetrates water..
The South Pole station operated by Stanford University has a antenna that is around 4 miles long & a few feet above the ice & despite this it still only achieves a 10% efficiency, I forget it's actual power levels, but a 100 watt TX would only produce about 10 watts erp due to the short antenna.
http://vlf.stanford.edu/vlfdata/index.php