Which shoe mostly worn by people such as ambulance and police workers became a 1970s fashion shoe?

Doc Marten Shoe.

Explanation:

This shoe was initially created by a doctor in order to accommodate the needs of the people in service industries.

In 1970s, this shoe was a standard issue among Police and Ambulance worker due to its durability. it can accommodate heavy used without being torn apart. More people became aware of its quality ever since that time period and people from outside the industry  started to use it for its fashion.