It passed through Kam Shan, the Shing Mun Reservoir, Beacon Hill, Lion Rock, and Tate's Cairn, ending at Port Shelter in Sai Kung District.

Its key points were the stretch between Beacon Hill and Sha Tin Pass, and the Shing Mun Redoubt, the latter of which also housed command HQ for the Line.

[6] Defensive headquarters were located at Shing Mun Redoubt (Chinese: 城門棱堡 or 城門碉堡) – also known as the "Strand Palace Hotel" – which had an observation post (acting as headquarters of the redoubt) that could call artillery support from Mount Davis battery and Stonecutters Island Fort, and four pillboxes (PB400-403) fitted with Vickers machine guns and Bren LMGs.

[7] There were 1.5 metre deep defensive channels or trenches, named after the roads of London such as Charing Cross, to aid the British soldiers of the Middlesex Regiment.

On the morning of 8 December 1941, Japanese forces bombed Kai Tak Airport, wresting control of the skies from the British and initiating the Battle of Hong Kong.

The success surprised Japanese commanders who had thought at least a month was required to break the British defences, and thereby diverted more forces from mainland China to boost manpower.

They also thought that a premature breakthrough would lead to rear forces and artillery troops falling behind, but ultimately agreed to launch a general assault.

Major General Christopher Maltby knew that the position was untenable and at noon decided to withdraw the garrison to Hong Kong Island to preserve its strength, signalling the defeat of the Line.

The Rajput Battalion stayed behind as a rear guard, only retreating on the morning of 13 December towards Devil's Peak and Lei Yue Mun towards Hong Kong Island.

The defensive structures left at Shing Mun Redoubt; and pillboxes at Lion Rock, Tate's Cairn, and Port Shelter have been damaged by gunshots and grenades by the British and the Japanese.

[7] In 2012, a group of scholars from the Hong Kong University mapped out the tunnels and their architectural characteristics, and called on the government to better preserve this historical heritage.