One of the surviving Observation Posts at Ynyslas, this one overlooking Cardigan Bay and the offshore firings that took place.The basic design for the shelters was referred to in a memo dating to February 1945 from the Walton-on-the-Naze Establishment, where scientists where working on a guidance system for the rockets (Brakemine Project). The two bays and two slits allowed up to 20 military personnel and scientists to view the test flights.