Naval Vessel Types in World War II
This section describes the various types of merchant vessel. These ships continued in their everyday tasks once war was declared, however all were exposed to the additional hazards of mines, torpedoes, air attack and surface attack without any meaningful protection of their own. Instead, they had to rely on others to protect them from harm.
The descriptions below of merchant ships are focussed on their design during the Second World War. Since then there has been a significant change in the arrangement of world shipping, with mass containerisation and massive bulk ore and oil carriers replacing the ships described below. Along with an increase in size has come a reduction in crew. It was not unusual to have a total compliment of 80 or more, whereas now it is not unusual to have a total compliment of about 25. Improved designs (with respect to both safety and cargo carrying capacity) have generally removed the central navigation bridge, and the aircraft has all but eliminated the passenger liner.
A tanker can be defined as: “A merchant ship, designed for the specific purpose of transporting liquid cargoes in bulk.” Tankers generally have their machinery spaces aft (at the stern, or back end, of the ship). Forward of this are the cargo tanks. These are numbered from forward to aft, with the number one tank being the furthest forward. Each tank is further divided longitudinally (from fore to aft) by one or more oil-tight bulkheads, so the vessel may have an arrangement such as port number one tank, starboard number one tank, and (perhaps) centre number one tank. This improves stability by preventing liquid sloshing from side to side when the vessel rolls. One or more pump rooms would be provided, and these are used for discharging cargo.
Tanks can be fitted with heating systems (to allow heating of heavy oils to enable them to flow), steam smothering systems (to put out a fire in the tank) and vents (to allow gas to escape). These vents would be fitted with flame arrestors on vessels where light oil cargoes were intended to be carried. At around the mid point of the ship would be the main superstructure, containing accommodation for deck officers, the navigation bridge and the radio room. The accommodation for the engineers would be at the stern, above the engine room.
During the Second World War, tankers were particularly valuable targets. Whilst the loss of general cargo vessels caused much concern, it was the loss of tankers that caused the most anxiety as they were being lost at a much greater rate. As the highest-value ships in a convoy, tankers were normally placed in the inner columns. This shielded them somewhat from attack, although the losses continued to be a problem until the Battle of the Atlantic was finally decided.
Tankers are difficult ships to sink. They are well subdivided in to watertight compartments, and are designed to carry a liquid of approximately the same density as water. If you put a hole in the starboard (right) side of the tanker, the oil will run out and the vessel will list (lean) to port (the left) whilst rising slightly out of the water as the weight of cargo is reduced. The vessel will only sink if structural failure occurs.
The main danger faced by crews of tankers was fire. Whilst crude oil is difficult to set alight (it is thick, often does not flow unless it is heated, and if a lighted match is dropped in to it the match will simply go out), refined products (such as petrol and aviation fuel) can be very flammable.
2. Passenger Liner:
A passenger liner may be defined as: “A merchant vessel designed for the main purpose of carrying passengers.” Passenger liners are usually fast ships, with a speed between 25 and 30 knots. Passenger liners were very different ships from the cruise liners of today. Their main purpose was to transport people between destinations, in much the same way as the airliner does today, rather than to provide a pleasant holiday experience. In the same manner as a modern airliner, passengers were split in to a number of classes. The first class passengers travelled in luxury, whilst the lowest class passengers were packed in as densely as possible.
The most important aspect of a passenger liner was its speed, with faster ships attracting more passengers and higher prices. This was because passengers simply wanted to get to their destination rather than enjoy the process of travelling. This obsession with speed fuelled great rivalry between the great liner companies, particularly on the prestigious North Atlantic route where the Blue Riband trophy was handed to the fastest ship to make the crossing.
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