Shire also considered this possibility: Could Colonel Estiny be a spy sent by Grevy?
If so, it would undoubtedly be a clever move by Grevy, as Estiny would learn the tank's design direction and even advanced combat theories from Shire.
But Shire believed Colonel Estiny was not a spy.
If he were, Grevy should have known the shortcomings of the CA-1 from Estiny and then prevented it from entering the battlefield.
Grevy does not lack money; he does all this to enhance the right-wing's influence on the military, and losing battles and being embarrassed is clearly contrary to this goal.
More importantly, Colonel Estiny is a historical celebrity known as the "Father of French Armor." He not only developed the CA-1 tank but also developed a heavy tank known as "Shire B1."