An assessment from a NSG member
From the UK Telegraph, which said that the planning for the Mumbai attack took a year:
one member of India’s National Security Guard, who led one of the assault groups against the terrorists occupying the Taj Mahal hotel, said they were the “best fighters” he had ever encountered.
He said: “They were obviously trained by professionals in urban guerrilla fighting. They used their environment and situation brilliantly, leading us (the NSG) on a dangerous chase through various tiers of the hotel which they obviously knew well. Their fire discipline too was excellent and they used their ammunition judiciously, mostly to draw us out.
“It was amply clear they came to kill a large number of people and to eventually perish in their horrific endeavour,” he said. “Negotiating with the Indian authorities or escaping was not an option for them.”
Bill Roggio has more on the training required for such a mission.