Short answers, pulled from the story.
The Colossus computer successfully decrypted its first message on the 5th of February 1944. This event marked the beginning of a secret war within a war that ultimately shortened the conflict by many months.
Tommy Flowers designed the Colossus computer and the prototype Mark 1 became operational on the 8th of December 1943. The prototype was then dismantled and shipped to Bletchley Park where it was delivered on the 18th of January 1944.
There were ten Colossus machines operational at Bletchley Park by V-E Day. An eleventh machine had started assembly but was not completed before the end of the war.
The existence of the Colossus computer remained a state secret until the mid-1970s. The secrecy was broken when Group Captain Winterbotham published his book The Ultra Secret in 1974 and Brian Randell presented a paper on the wartime development in 1976.
The reconstructed Colossus Mark 2 is displayed at The National Museum of Computing in H Block Bletchley Park in Milton Keynes, Buckinghamshire. The reconstruction was built between 1993 and 2008 by a team led by Tony Sale.