your knowledge of military strategy makes me want to laugh and cry at the same time.
laugh because its ridiculous, cry because it will destroy the environment
modern oil tankers have double hulls.
in order to accomplish the objective (block a Canal or strait), all you need are a half dozen semi-competent frogmen with limpet mines
pick a tanker that's riding low in the water (full of oil), use a speed tester to get the tanker's speed, set the timer on the limpet mines, plant the aforementioned mines, escape to a safe distance and then watch as the explosions blow out the outer hull and sinking the tanker right in the middle of the Canal
remember, we want to destroy the enemy not destroy the environment along with them