The London Monitor is the boss fight at the very end of lvl 14. To Kill it you must first go into the tunnel system and find a power conduit to charge your LKW.
First wait until it charges it's eye beam, it'll make an audible screech each time and glow Red. Shoot it's eye and get ready to shoot one of the 6 rocket pods on it's shoulders. You'll have to repeat these steps until all are destroyed.
Once all 6 are destroyed you must then again shoot it in the eye and then run underneath it. Then shoot into the engine which will be exposed, after the second go you should be done.