Complex sentence: Other users were the I ANZAC Corps in Egypt and later on the Western Front, II ANZAC Corps on the Western Front and the 1st (ANZAC) Wireless Signal Squadron, which served in the Mesopotamia Campaign.
Split into simpler sentences: Other users were the I ANZAC Corps in Egypt and later on the Western Front, II ANZAC Corps on the Western Front. The there was the 1st (ANZAC) Wireless Signal Squadron, which served in the Mesopotamia Campaign.