It's the latest in a range of elaborate tactics the militants are using as they try to cling to the city, their last major urban stronghold in Iraq. They have dug extensive tunnel networks to avoid airstrikes, planted roadside bombs and sent hundreds of car bombs toward advancing forces.
Although the Iraqi military has come across most of those methods before as they have slowly taken back territory from the militants, it is the first time they have seen the decoys.
Safaa al-Assam, an Iraqi military analyst, said the effort shows that Isis is planning for a long-term battle and will not give up on Mosul easily. The replicas "are made to distract warplanes from the real targets, as well burdening the Iraqi air force and the international coalition".
Isis militants seized huge caches of weapons from the Iraqi army when they took over Mosul 2 years ago. Iraqi Prime Minister Haider al-Abadi has said that the military lost 2300 Humvees alone.
With so many, the militants have used the armoured vehicles for suicide bombings because they are harder for ground forces to stop with small-arms fire.
Brigadier General Yahya Rasool, a spokesman for Iraq's joint operations command, said the use of decoys "means that this is the beginning of their end" for Isis.
It is unclear whether the military would be able to know if decoys had been hit.