Before the Second World War started in 1939 many German citizens who had professional skills were allowed to enter Britain. After the war started the British government decided to intern them all until their individual cases had been investigated by internment tribunals, to determine which ones might be a threat to national security. Consequently Eric Zepler was interned on the Isle of Man for 10 months from early in 1940. Meanwhile the RAF and the Luftwaffe were intensifying their operations, both of them using radio equipment based on his designs.

The internees on the Isle of Man included scientists, engineers, writers, artists, musicians, and so on. To occupy themselves they formed an informal university where they pursued their professional interests and participated in courses on many subjects. Eric Zepler gave courses on electronics and radio design, and started to write his classic book entitled The technique of radio design.

When Eric Zepler was released from internment he started teaching in the Engineering Department at the Technical College in Shrewsbury, and continued working on his book.