After the government asked the armed forces to get ready, India's Southern Command fielded the 17th Infantry Division and the 50th Parachute Brigade. The assault on Daman was assigned to the 1st Maratha Light Infantry while the operations in Diu were assigned to the 20th Rajput and 4th Madras battalions. Air resources for the assault on Goa were concentrated in the bases at Pune and Sambra.
Operation Vijay saw the Indian Navy deploy two warships — INS Rajput, an 'R' Class destroyer, and INS Kirpan, a Blackwood class frigate, off the coast of Goa. The actual naval assault was assigned to four task groups - a surface action Group comprising five ships (Mysore, Trishul, Betwa, Beas and Cauvery), a carrier group of five ships (Delhi, Kuthar, Kirpan, Khukri and Rajput centred around carrier Vikrant), a mine Sweeping Group and a support group.
Salazar, disregarding other officials and military officers, asked the Portuguese authorities in Goa and there would be no surrender and that Portugal should fight till the last man. He asked the Portuguese forces to at least hold out for eight days which he thought was enough time to garner international support against 'Indian invasion'.
Portuguese ground defences consisted of 3,995 men, including infantry troops and 810 Goan soldiers. In addition, there were about 1,040 police officers and 400 border guards divided among the three Portuguese enclaves in India. The strategy employed to resist Indian invasion was centred around the Plano Sentinela which divided Goa into four sectors, with forces assigned to each sector and tasked with slowing the progression of an invading force. These plans were however unviable because of the desperate shortage of ammunition and communication equipment.
One Portuguese Navy ship, Afonso de Albuquerque, was present in Goa at the time of invasion. The vessel was armed with four 120 mm guns capable of two shots per minute and four automatic rapid firing guns. There were five merchant navy ships in Goa and three light patrol boats, each armed with a 20mm Oerlikon gun.
Commenting on the Plano Sentinela, Captain Azaredo told Portuguese newspaper O Expresso in 2001, "It was a totally unrealistic and unachievable plan which was quite incomplete."
On December 18, Indian Air Force Canberras pounded the Dabolim Airfield, rendering the runway invalid but causing no damage to infrastructure and facilities. Another raid by Hawker Hunters neutralised a wireless station at Bambolim.
On December 18, under covering fire from INS Trishul and INS Mysore, Indian troops landed on the island of Anjidiv and engaged the Portuguese defenders. The Portuguese ceased fire and raised a white flag, thus luring the Indian soldiers out of their cover before opening fire again, killing seven and wounding 19. The Portuguese defences were eventually overrun after fierce shelling from the Indian ships offshore. The island was secured by Indian troops by December 19.
On the morning of 18 December, Afonso de Albuquerque was anchored off Mormugao harbour. Three Indian frigates led by the INS Betwa took up position off the harbour at 9 in the morning. At 11 AM, Indian planes raided the harbour and at 12.00 pm, INS Betwa, accompanied by INS Beas, entered the harbour and opened fire on the Portuguese ships with their 4.5-inch guns while transmitting requests to surrender in between shots in morse code. In response, Afonso de Albuquerque lifted anchor, headed out towards the enemy and returned fire with its 120 mm guns.
A few minutes into the exchange of fire, the Afonso took a direct hit in its control tower, injuring its weapons officer. At 12.25 pm, an anti-personnel shrapnel bomb fired from an Indian vessel exploded directly over the ship, killing its radio officer and severely injuring its commander, Captain António da Cunha Aragão, after which First Officer Pinto da Cruz took command of the vessel. The ships propulsion system was also badly damaged in this attack.
At 12.35 pm, Afonso de Albuquerque swerved 180 degrees and was run aground against Bambolim beach.
Eventually at 12.50 pm, after having fired nearly 400 rounds at the Indians, hitting two of the Indian vessels, and having taken severe damage, order was given to abandon the ship. In all, Afonso de Albuquerque lost 5 men and 13 were wounded in the battle.
The 50 Para Brigade moving in from the north and the northeast on December 18 was the first to reach Panjim on December 19. The Aguada fort was run over and Portuguese forces were overrun and many surrendered.
Meanwhile from the east, the 63rd Infantry Brigade marched on Margao. On the way fell Ponda, Candeapur and Darbondara. They then continued till Dabolim Airport and Mormugai harbour.
By the evening, most of Goa had fallen to advancing Indian troops and the Portuguese had gathered around 2,000 soldiers at the entrance to Vasco da Gama to make their last stand.
The instruction from Salazar was to hold out at the harbour till naval reinforcements arrived from Lisbon. But Goa's Portuguese Governor General Manuel António Vassalo e Silva took stock of the numerical superiority of the Indian troops, as well as the food and ammunition supplies available to his forces and took the decision to surrender. He later described his orders to destroy Goa before losing as "um sacrifÃcio inútil" (a useless sacrifice).
In a communication to all Portuguese forces under his command, he stated, "Having considered the defence of the Peninsula of Mormugao"¦ from aerial, naval and ground fire of the enemy and "¦ having considered the difference between the forces and the resources"¦ the situation does not allow myself to proceed with the fight without great sacrifice of the lives of the inhabitants of Vasco da Gama, I have decided with "¦ my patriotism well present, to get in touch with the enemy "¦ I order all my forces to cease-fire."
The official Portuguese surrender was conducted in a formal ceremony held at 2030 pm on December 19 when Governor General Manuel António Vassalo e Silva signed the instrument of surrender bringing to an end 451 years of Portuguese Rule in Goa. In all, 4668 personnel were taken prisoner by the Indians - a figure which included military and civilian personnel, Portuguese, Africans and Indians (Goans). Of these, 3412 prisoners were taken in Goa, 853 in Daman and 403 in Diu.
