In a nutshell, that line was built from the end the OR&L line at Schofield Barracks to connect with the OR&L main line on the north shore near Haleiwa. Very few, if any, trains other than construction or crew training ever used the line. It was built during WW2 to be used in the event that the main line along the leeward side of the island and around Kaena Point was damaged by a Japanese attack or a tsunami. Chiddix and Simpson have a good deal more info in their book "Next Stop Honolulu".
It is known that the OR&L did use some of the plantation lines to access ammunition storage dumps. This is also discussed in Chiddix and Simpson's book.
Ed
Edited 2 time(s). Last edit at 12/07/2016 08:48AM by Ed Stabler.