The Japs also wanted to nuke the obstacles to clear the Isthmus
Anyway, i believe the Isthmus of Kra is possible within the next 30 years as oil and gas get scarcer and the pressure to create shorter and faster trading routes. Our 'special' geographical position that is always emphasized by PAP to no end will not save us, we are beginning to enter the end of our successful maritime industry. :(
Faster PIPELINE.
Thai will connect pipe from Myanmar to Vietnam and Malaysia also parallel with Isthmus to connect East and West Thai. All solve. Cost less than 5%.
