I believe that this is a Remote-Controled Water Cannon on Fire Ladder.
On June 2 2011, two San Francisco firefighters, Vincent Perez and Anthony Valerio, were killed in a house fire. It was the San Francisco Fire Department's deadliest call in 65 years.
On June 10th 2011, a funeral procession of about 500 firetrucks from all over California, escorted by motorcycle Police, carried the fallen firefighters from St Mary's Cathedral to the cemetery. I took this photo at this event.
For more informations about this event, read this article on the San Francisco Chronicle.
Unclassified photos taken in San Francisco Bay Area.