Definition: In this task, you need to generate an appropriate title for the given summary of some paragraph. The generated title must be short and should include the main topic of the given text. Your summary should be less than 20 words long.
Input: MPs have backed building replacements for the UK's Vanguard fleet of four submarines carrying Trident nuclear missiles. The subs are due to become obsolete by the end of the next decade.

A guide to Trident and the debate about replacement