A mobile oil platform parked offshore at Nairn
I often see oil and gas platforms 'passing by' on their way to and from the Cromarty Firth (just at the other side of the Moray Firth from here), where they come for repair and maintenance at Invergordon every so often, but they are generally moved by one or more tugs. This version appears to be somewhat different, however, being itself a sea-going vessel. I am assuming the tall legs, currently seen above the vessel, are gradually lowered into the sea with the ship part of the vessel being 'cranked-up' the legs as it moves into deeper water, with the legs eventually resting on the sea bottom - comments from anyone more kmowledgeable than me about this kind of vessel will be welcome.
The Cromarty Firth used to be one of the major safe harbours for the Royal Navy, long before the oil industry became important in the UK. The other safe haven for the British Fleet in this part of the country was at Scapa Flow in the Orkney Islands. Incidentally, the German Imperial Navy was interned at Scapa Flow after the Armistice at the end of the First World War and later scuttled by its own personnel.