<span style="color: #222222;">United States President Donald Trump has announced that he will replace Defence Secretary Jim Mattis with his deputy Patrick Shanahan as acting Pentagon chief on January 1. <br />''<br />''US President announced the replacement of the Pentagon chief two months earlier than Mattis' planned departure. In a tweet, Mr Trump said, Patrick has a long list of accomplishments while serving as Deputy, and previously Boeing and he will be great. Mr Mattis announced his resignation on Thursday with a letter saying his views were not aligned with Mr Trump.</span><br />