being received in 1800. Shipping in the Port of London supported a vast army of transport and warehouse workers, who characteristically attended the "call-on" each morning at the entrances to the docks to be assigned work for the day. This type of work was low-paid and highly unstable, drying up depending on the season and the vagaries of world trade. The poverty of the dock workers and growing trade union activism coalesced into the Great Strike of 1889, when an estimated 130,000 workers went on strike between 14 August and 16 September. The strike paralysed the port and led the dock owners to concede all of the demands of the strike committee, including a number of fairer working arrangements, the reduction of the "call-on", and higher hourly and overtime wages. Shipbuilding During the first half of the 19th century, the shipbuilding industry on the Thames was highly innovative and produced some of the most technologically advanced vessels in the world. The firm of Wigram and Green constructed Blackwall frigates from the early 1830s, a faster version of the East Indiaman sailing ship, while the naval engineer John Scott Russell designed more refined hulls for the ships constructed in his Millwall Iron Works. London shipyards had supplied about 60% of the Admiralty's warships in service in 1866. The largest shipbuilder on the Thames, the Thames Ironworks and Shipbuilding Company, produced the revolutionary broadside ironclad HMS Warrior (1860), the largest warship in the world and the first iron-hulled, armor plated vessel, alongside its sister HMS Black Prince (1861). Over the next few years, five out of the nine armored ironclads commissioned by the Navy to follow the example of the Warrior would be constructed in London. The Thames Ironworks was employed not just in shipbuilding, but in civil engineering works around London like Blackfriars Railway Bridge, Hammersmith Bridge, and the construction of the iron-girded roofs of Alexandra Palace and the 1862 International Exhibition building. London engineering firms like Maudslay, Sons and Field and John Penn and Sons were early developers and suppliers of marine steam engines for merchant and naval ships, fueling the transition from sail to steam powered locomotion. This was aided by the 1834 invention by Samuel Hall of Bow of a condenser for cooling boilers which used fresh water rather than corrosive salt water. In 1838 the first screw-propelled steamer in the world, SS Archimedes, was launched at Ratcliff