I think this may be why the Brits were there. Protection.
"Al Faw Petroleum Enterprises, Basrah - Iraq
On the terrains of Al Faw on the banks of the Shatt Al Arab river an oil jetty is built next to Abu Fluss.
Al Faw has a fleet of oil barge tankers with full equipment incl. generators. On each barge are 4 pumps available with a capacity of 250 ton per hour each. Al Faw has also service tugboats to their disposal and supply boats, crew boats etc., all appropriate for services.
In general the oil barges are used to bring the product from different sources in Basrah (El Basrah, El Muftea Oil Terminal (on the Shatt Al Arab river)) to open sea or to Khor Lzubeyr and Umm Qasr, but also to supply to places near Al Bakr Terminal and Al Amaya Terminal.
Al Faw has also a floating oil terminal, which a capacity of 5,000 ton product, fully equipped with a pump system of 1,000 tons per hour and with accommodation facilities too."
Well there certainly is some good stuff to protect on the Iraqi side of the line.
Wonder what might be on the Iranian side of the border?