The Hammer Channel Tunnel is a tunnel project put forth by Justin Hammer. It connects London with another unknown location. It's Ribbon Cutting Ceremony was to begin when Big Ben struck 12 noon. At the ceremony they were attacked by Radioactive Zombies from the Russian submarine Prometheus. Force Works had to come to the tunnel and save the civilians. Titanium Man eventually came but was stopped by Iron Man. Eventually the Prometheus Crew were cured and returned to normal.
The tunnel appears to be analogous to the Channel Tunnel linking England and France, which opened four months before the episode aired. Though in Iron Man it opens onto London, quite far from the real tunnel.