The Seagull trench is a trench in the form of a flattened 'W' with a flat concrete roof covered in turf, supported on concrete pillars. The name derives from the resemblance to a child's drawing of a seagull in flight. This photo shows the beach it was defending, looking approximately in the direction it faces. It was very well positioned. RAF Llandwrog (as it was) is ahead, to the right.
Many thanks to Chris, Webmaster Staffshomeguard.co.uk for photos and text