Good read:

In the summer days starting from 24 August, Ukraine’s Independence Day, to 29 August 2014, Ukrainian army and volunteer battalions found themselves entrapped by Russian forces near the small town of Ilovaisk. A plan to let the Ukrainians escape was negotiated with the Russian side, but the latter opened fire at the last moment, killing 366.

In those red-hot August days of 2014, it seemed that Ukraine’s anti-terror operation against Russian-backed militants in eastern Ukraine, which was into its fifth month, would be finished in a couple of weeks, considering the rapid, successful advancements of the Ukrainian Army in all directions. . . .

The investigation claims that Ukraine was invaded by nine battalion tactical groups of the Armed Forces of the Russian Federation:

about 3500 personnel;
60 tanks;
320 AFVs and APCs;
60 howitzers;
45 mortars;
5 anti-tank guided missiles.

As a consequence of the invasion, the volunteer battalions along with units of Armed Forces of Ukraine were trapped in Ilovaisk. The General Staff had no real reserves to send there to help the besieged. There were only two possible options – to fight their way out or lay down the arms. The commanders of ATO forces chose the second one.

The investigation confirms that Viktor Muzhenko, the Chief of the General Staff, started negotiating with the deputy chief of the General Staff of the Russian Federation Nikolai Bogdanovsky to grant safe corridors for the escape of Ukrainian military units. There were 12 phone calls between them. Russia agreed to guarantee the safe passage by the negotiated routes.

On August 29, when the convoys of ATO forces began to move, the Russian soldiers shot them down like at a shooting range. Additionally, the Russian party had been constantly changing the exact time of the Ukrainian forces’ withdrawal in order to buy time to prepare their firing positions. Ukrainian soldiers who survived gave much evidence to this fact.

As a result of the sneak attack:

366 Ukrainian soldiers were killed;
429 were injured;
300 were taken prisoner;
later, the majority of the prisoners were exchanged, eight are still kept in the basement prisons in Donetsk;
the military hardware losses of the Armed Forces of Ukraine are estimated at $12 mn.

http://euromaidanpress.com/2017/08/23/probe-into-ukraines-largest-military-defeat-at-ilovaisk/