The strategic importance of Lei Yue Mun, as the entrance to the inner harbour of Hong Kong, is obvious. The construction of defence installations was considered in the 1880s to protect Hong Kong from possible threats posed by Russia and France. A redoubt, several batteries, underground magazines and a torpedo station were then built. Lei Yue Mun at this time was considered virtually invulnerable to attack. However, by the First World War, the defensive importance of Lei Yue Mun had declined considerably as a result of the installation of the powerful 9.2 inch breech loading guns at Devil's Peak covering a greater range on the eastern sea approach. These military remains have been restored as a Historical Trail where visitors could appreciate these historical remains and picture the military strength of Lei Yue Mun Fort a hundred years ago.