The army vehicles were travelling in convoy in Lincolnshire when they crashed yesterday.
Another lorry travelling behind the convoy was also involved in the smash but it has not yet been revealed what caused the incident, which left a number of drivers trapped.
Lincolnshire Police said today that a 56 year-old South Yorkshire man is in a critical condition in the Queen’s Medical Centre, Nottingham and a 44 year-old man, also from South Yorkshire, is being treated for serious injuries in Addenbrooke’s Hospital, Cambridge.
Both men were drivers of the MOD vehicles.
The driver of the articulated lorry, a 23 year-old man, remains in hospital.
All three men were airlifted to hospital after being freed from the mangled wreckage of their vehicles.
A police spokeswoman said the South Yorkshire men are civilian contractors who were driving the military trucks from one base to another.
Luke Spencer, who works close to the crash scene on thee A17 near Swineshead Bridge, Boston, said: “We heard it. It was a screech, a bang and then loads of screams.
“It was like a bomb going off.”
Firefighters spent hours cutting the casualties free from the lorries.