This medieval chapel sits in the middle of the Castlemartin Royal Armoured Corps firing range. It contains a single nave and chancel with a small lean-to chamber on the north which has been used as a vestry. The bell-turret to the west was added in the late fifteenth or sixteenth century. It has large openings on all four sides and inside there is a semi-circular bell-rope shaft. The chapel was used variously as a carpenter's shop, stone shed, granary, and cart house from the late-eighteenth century, and blocked cart-entrance arches from this time are still visible. It was restored and rededicated in 1901-3 by Col. Francis and Lady Victoria Lambton when an entrance porch was added to the north side, to the west of the small lean-to room. There are several memorials to members of the Lambton family both inside and outside of the chapel, including images of two angels under pointed stone arches holding banners reading `BUILDING UP YOURSELVES ON YOUR MOST HOLY FAMILY? and `TO DO GOOD AND TO DISTRIBUTE FORGET NOT'. Under the left angel the caption reads `In most loving memory of Victoria Alexandrina Lambton daughter of the Second Earl Cawder and wife of Lt Colonel Francis Lambton. Born 24th Mech 1843. Died 30th March 1909. She worked for many years with others to provide Queen Victoria Nurses for the poor in their homes.? In the churchyard there are several large boulders with were moved there from various locations in the vicinity to save them from destruction. In the churchyard there is also a Celtic cross on four steps which was erected by Clarke of Llandaff in 1909.

(Sources: Inventory of the Ancient Monuments in Wales and Monmouthshire VII. County of Pembroke, Vol. I (RCAHMW 1925), p. 65; Lloyd, Orbach, and Scourfield, The Buildings of Wales: Pembrokeshire (2004) p. 163; RCAHMW Colour Transparencies C422763; Cadw listed buildings database)

A.N. Coward, RCAHMW 12.04.2018