LONDON, UK — It's just after 8 a.m. at Finchley Road station on the Metropolitan line and London's subway network is heaving with rush hour passengers. For most this is just the start of another working day. But for the transport network through whose maze of narrow tunnels they have rattled, it is a phenomenal feat: more than three million people delivered safely, without delay. The London Underground, or Tube as it is more commonly known, is today celebrating its 150th anniversary. Some of the tunnels, including those used by the Metropolitan line, have been in near-continuous operation since steam trains first navigated them in 1863.