The Battle of Trafalgar was fought between British and Franco-Spanish fleets on 21 October 1805. A force of 27 British ships of the line faced 33 allied ships. Both forces were formed in two columns; the British sailed parallel, the allied one following the other. The Battle of Trafalgar was fought by sailing vessels and therefore cannot be understood in substance except as the manoeuvring of sailing vessels according to the principles of sailing. Without understanding the importance of wind and weather, especially wind direction, the modern can make no sense of the manoeuvring. Once those principles are understood, the plan of battle unfolds in a transparent fashion. The plan is included here as well as its general applicability to real events. Real battles do not always develop according to plan, or exactly according to plan. Commanding officers usually are empowered to respond to the battlefield situation as it develops. Such concepts as "sailing order" and "battle order" are constructs. In a column of ships sailing anywhere the first ship forward was Number 1, the second, Number 2, etc. The battle order was based on planned order of attack. Ships were assigned places in these orders by the commander, sometimes temporarily or even extemporaneously. Nelson used the order that was best momentarily. In stormy weather or other adverse conditions the commanders might not be able to control the order. "Nelson's fleet" was not a fixed entity; ships were continually joining or leaving his fleet for various reasons: for example , was in the docks being repaired after four years at sea, including the chase of Villeneuve and was daily expected to re-join the fleet, where her Captain, Richard Goodwin Keats was to be Nelson’s second, but she was not repaired in time. The complements of the ships also were variable. The early historians of the battle were not sure of what they were, nor did they know exactly what the casualties were. The roster lists of the ships before sailing were generally used. Afterward there were plenty of reports. The numbers and orders of this article are based on the figures of modern scholars for the most part. There is general disagreement on the exact order and the exact numbers, but, on the whole, the different estimates are close to each other and can probably be taken as accurate within a few per cent. An effort is made to keep