 Complete the following phrase:  In 1900 Heugh was completely reworked for two 6-inch Mk VII guns using the standard configuration of two emplacements with underground magazine between. The defences were further modified in 1907 when the Lighthouse gun was replaced with a 6inch Mk VII and the Cemetery Battery closed. Manned by the Territorial Force gunners of the Durham Royal Garrison Artillery, these were the three guns that were to see action in the 