Brutus 155mm truck-mounted howitzer

[TomS]

The Indian Bharat MGS 155mm L39 is going to beat up the barrel as it travels. It may be preferable to shoot facing away from the cab, but your vehicle center of gravity shifts away from the center of the vehicle. All that mass on a long barrel is going to whip about and oscillate like mad during travel. Having a storebar over the cab keeps your mass more centralized and minimizes these same forces.

There's a travel lock above the cab in that image of Bharat. So, while it may fire facing away from the cab, it drives with the barrel forward and clamped down.

 

[MadRat]

Oh, I missed that.