How many bombing shelters were made in world war 2?

During World War II, millions of bombing shelters were constructed across Europe and other affected regions to protect civilians from air raids. In the UK alone, the government built around 1.5 million Anderson shelters and hundreds of thousands of Morrison shelters. Additionally, many countries implemented various types of shelters, including reinforced buildings and underground facilities, depending on their specific needs and resources. The total number of shelters globally is difficult to quantify precisely due to varying definitions and local efforts.