Flight to Dungavel - Murphy, Huff & Palmer, #1

In 1918 a sergeant saves the life of a pilot who crashes in no-man's-land. After the war the two ex-soldiers construct a bootlegging empire. To account for their illegal income, they finance two engineers who claim to have discovered diamonds in British Guiana. Certain the venture will fail, they 'cook' the books to show income from the mine. In 1933 they are forced to flee the country. In British Guiana they find the mine is successful and take an active role-they buy a British Avro, hack an airfield out of the jungle, and fly supplies to the mine.
In 1934 the mine produces an enormous cache of diamonds. The sack of diamonds is loaded aboard the Avro that crashes in an unexplored, inaccessible area of Guiana populated by aborigines. The fact that diamonds were aboard is closely held. In 1940, Hitler learns that diamonds were aboard the biplane and orders the SS to recover them. Churchill learns of the plan...