Radio antenna at Flamborough Lighthouse

By the fog horn at Flamborough lighthouse there is what I think is a dipole antenna - ie a T-shaped wire - suspended between the two masts that you can see in the picture. I estimate that the masts are 20 metres apart. The top of the T for a dipole antenna is half a wavelength. So the wavelength would be 40 metres. Frequency = speed of electromagnetic waves/wavelength = 15 MHz. This seems to come in the High Frequency (HF) band as opposed to VHF. This sounds correct because https://en.wikipedia.org/wiki/High_frequency gives HF as used for maritime sea-to-shore communication and http://info.yachtcom.co.uk/HF-frequencies/ lists similar frequencies.