Hi all,
As the Tank Americaine was launched in 1989, the timepiece that Rex Harrison is wearing is more than likely either a Tank Cintree or a Curved Tank. The 1920's/1930's versions of the Tank Cintree are beautiful examples of early 20th century Cartier watchmaking.
A very comprehensive history and documentation of the evolution of the Tank watch is provided in The Tank Watch book by Franco Cologni.
CK