Bayinnaung now looked to Siam, which successfully fought off the first Burmese invasion in 1547-1549. However, Bayinnaung now had a far larger empire at his disposal. Knowing that Siam be much more difficult than Shan states and Lan Na campaigns, Bayinnaung assembled the largest army yet—60,000 men, 2400 horses and 360 elephants, two and a half times larger than his previous high. The army would have been larger but the ruler of Chiang Mai, Mekuti, did not send in his share of the levy. Four Burmese armies invaded northern Siam in November 1563, and had overcome Siamese stands at Kamphaeng Phet, Sukhothai and Phitsanulok by January 1564. Armies then came down on Ayutthaya but were kept at bay for days by Portuguese warships and batteries at the harbour. Siamese defences collapsed after the Burmese captured the Portuguese ships on 7 February 1564 . King Maha Chakkraphat of Siam surrendered on 18 February 1564 . The king and crown prince Ramesuan were brought back to Pegu as hostages. Bayinnaung left Mahinthrathirat, one of Maha Chakkraphat's sons as vassal king, along with a garrison of 3,000 men.
Question: How many years was the first Burmese invasion?
Answer: 2