I thought that the "commander" of the vehicle did that job, at least for the US.
When the vehicle is not in action and it is time to have a sleep it is generally standard procedure to guard the vehicle from the outside, with each crewman taking a turn. In a platoon of 4 Soviet or Russian tanks that means 12 men to share guard duty.... 4 less than a western unit... because of the autoloader.
It was a stupid move, I've heard that its main fault. (The 115)
From people who claim smoothbores are inaccurate, yet the modern Abrams with its German smoothbore can hit the balls of a fly at 4km range?
Yeah, but rifling has its own advantages as well.
Only for HE shells... which is why the 100mm gun of the BMP-3, which is specifically designed to fire HE rounds as standard and also artillery weapons like 152mm and 155mm artillery also use rifled barrels.
For a tank gun it is much more expensive to make and more difficult to keep clean and it needs to be longer and heavier than an equivalent smooth bore and in terms of HEAT and APFSDS round it REDUCES their performance dramatically.
No level of tight rifling will impart enough spin to stabilise a javelin or a dart or an APFSDS projectile... they simply can't be spun fast enough to properly stabilise in flight so small fins are used instead.
With the HEAT round the problem is the focused beam of plasma the shaped charge is creating... centrifugal force rips it apart and makes it less effective on target because it is trying to spread instead of trying to concentrate like it should.
Again fin stabilisation keeps the round on target to a degree that is good enough, while the performance improvements were substantial.
The only round that likes being spun is the HESH... an obsolete round still in use by the British requiring them to cling to their out of date rifled guns.
Against a hard target HESH is defeated easily with spaced armour... as used on most modern tanks as standard armour and available as an add on package of armour aplique.
Evidence is shown when pride of the British Army Challenger tank mistakenly fires on British Army Warrior IFV. Warriors super armour protects it from super deadly weapon. In actual fact standard armour upgrade for light vehicles defeats obsolete British tank round.
The HESH round needs to be spun in flight for stabilisation but when it hits a target it splatters and then detonates sending a huge shockwave through the armour it hits.
A WWII tank would find the inner armour of their vehicle scabbing off and bouncing around inside the tank with lethal effect on crew, ammo, and fuel... very hot razor sharp metal fragments flying around the crew compartment at supersonic speed...
Of course anti spall linings are standard and have been for half a century, while any cavity in the armour stops the shockwave dead.