On 11 February 1727 Spain, under command of the Marquis de las Torres and supervision of Chief Engineer of the Spanish Royal Engineer Corps Marquis of Verboom, laid siege to the city . Depending on the sources, Spanish troops were between 12,000 and 25,000. British defenders were 1,500 at the beginning of the siege, increasing up to about 5,000 by troops brought from overseas by a fleet commanded by Charles Wager. After a four-month siege, with several unsuccessful and costly attempts, Spanish troops gave up and retired on 12 June. Spain had lost over 1,400 men while the British had suffered around 300 casualties. The Spanish had expected material help from the Austrians promised under the Treaty of Vienna, but they received little. They had been outmanoeuvred by British diplomats, who had concluded a secret deal with the Austrians to prevent them intervening.
Question: The number of Brittish fighters increased by about how many?
Answer: 3500