The national capital was under an unprecedented security blanket on Tuesday with the Red Fort, where Prime Minister Manmohan Singh unfurled the national flag and addressed the nation, converted into an impregnable fortress.
All roads leading to the historic monument were heavily- barricaded and vehicles were subjected to intense checks at several points in the wake of terrorist threats to sabotage the celebrations.
Quick Reaction Teams and commandos of Delhi Police, ITBP and the National Security Guard (NSG) were deployed at strategic locations, while a 10,000-strong security cover was given to the Red Fort.
People going to the Mughal monument were subjected to frisking at various points as a multi-tier security ring was thrown in and around it, one of the reasons for many empty seats at the venue.
IAF helicopters hovered over the Capital during the function while sharp shooters took positions atop around 500 buildings in the vicinity of the Red Fort in the crowded Old Delhi area as the day was celebrated amid increased "threat perception" following the Mumbai blasts.
Sniffer dogs were also pressed into service to check any explosives at the venue in view of "general and specific" intelligence inputs about terrorist plans to target "prominent political leaders and symbols of national importance".
The city was in a state of "high alert" as an elaborate ground-to-air security apparatus was in place, including deployment of anti-aircraft guns, to thwart possible attempts to subvert the celebrations.
Special focus was given on anti-sabotage and anti-explosive checks and tight access control measures were in place at the Red Fort.
The airspace over the Capital was closed from 5 am to 9 am as radars of the civilian air traffic control and Indian Air Force scanned the airspace to ward off possible aerial attacks using unmanned or microlight aircraft.
No vehicular movement was allowed in the vicinity of the Red Fort and trains passing near the venue were diverted since early morning till the function concluded.
Besides the Red Fort, security was also tight at all sensitive areas in Lutyens Delhi, vital places like the Indira Gandhi International airport and Parliament and crowded areas including bus terminals, railway stations, metro stations, markets and cinema halls.
Delhi Police had mobilised its entire strength for the Independence Day function and specialised units like Special Cell and Crime Branch were keeping a tight vigil.
Security was also beefed up at metro stations, a prime target for terrorists, and the New Delhi railway station.
Parking of vehicles at Metro stations and the main railway stations was banned from 10 pm Monday night to 12 noon on Tuesday.
Entry of heavy vehicles was banned in the Capital since Monday night.