The Jurong-Kranji Defence Line was one of two fall-back positions meant for the withdrawal and consolidation of troops, should the Japanese forces overcome the coastal defending forces in Northwest Singapore.
The lack of preparation of the Jurong-Kranji Line, and the large area to be covered meant that troops had to be spread out very thinly along the Defence Line. Miscommunication and uncoordinated initiatives at the senior commanding level on 10 February 1942 made the problems worse.
Brigadier Taylor of the 22nd Australian Brigade misinterpreted instructions and prematurely withdrew his units from the Line back to the last-ditch defensive perimeter around the city. This set off other withdrawals along the Line, leaving the position largely undefended against the advancing Japanese.
By the afternoon, the Line was in Japanese hands. This forced the withdrawal of all allied forces in the North and East to the city perimeter.
There was also an equivalent of the Jurong-Kranji Defence Line on the east which was the Serangoon Line, stretching from the Serangoon River to the southeast coast.Google Map Link