The Sir Galahad window is thought to be one of the few church windows to show the Holy Grail (others include the Tennyson Memorial Window in St Bartholomew's in Haslemere and an almost identical representation in All Saints, Marsham in Norfolk).
The window, as were all the windows on the north and south sides of the nave, were executed by James Powell & Sons of Whitefriars at the Strand (renamed the Whitefriars Glass Company in 1921). This was one of the oldest glass companies in London; its trademark is a small figure of a white friar which can be seen in the lower right margin of the window.
According to the Arthurian legend, Sir Galahad is the knight who finally saw and beheld the Grail. He is depicted in this window with the Sword of David which he retrieved from a river earning himself a place at the Round Table as the greatest knight. The lower portion of the window depicts him riding out on his white steed with white pennant flag billowing.
The dedication reads: "In beloved memory of my husband Guy Macaulay Mort D S O Lt Col 8th Hussars + So he passed over all the trumpets sounded for him on the other side + 27th December 1923".