 Complete the following phrase:  After the First World War, the 51st Sikhs were grouped with the 52nd, 53rd and 54th Sikhs, and the two battalions of Guides Infantry to form the 12th Frontier Force Regiment in 1922. The 51st Sikhs became 1st Battalion Prince of Waless Own Sikhs of the new regiment. During the Second World War, 1 FF saw active service in 