

The Ipcress File
The Man Who Would Be King
The War Lord
Panic in Year Zero
Dr. Strangelove or: How I Learned to Stop Worrying and Love the Bomb
or the more serious counterpart:
Fail Safe
Colossus: The Forbin Project
Threads (1984) - not so old, but belongs here with those other nuclear war films.
The Andromeda Strain
Aluminium conducts better per weight. Copper per volume.