DavidPawley said:

Engineers are vehicle crew? I must let my engineer acquaintances know that.

Just a few examples.

I don't know how you think modern engineers do their work? Lots of people with shovels?
The main mode of transportation of the German engineers is the Fuchs APC.
Except for the speciality engeneering companies of the airborne and mountain brigade the engeneering units are all fully mechanised.

mpopenker said:

Position of the slung weapon may be dependent on the chances of the enemy infantry suddenly popping out near your position

Looking at pictures with German troops from WW2 it mostly seem to depend how official the picture was. The staged, official propaganda pictures allways show soldiers in perfect uniform with rifle on the back. The snap shots taken during combat allways show very sloppy uniforms and no small arms nearby.

I took a look at the Soviet artillery photos from the WW2:

as you can see, it's a fair mix of people with and without small arms. I think the larger artillery caliber is, the less you will see small arms around it.

At least, most Soviet 45mm and 76mm AT crews are shown carrying their issued small arms during the action, which should be of little surprise, I think

mpopenker said:

At least, most Soviet 45mm and 76mm AT crews are shown carrying their issued small arms during the action, which should be of little surprise, I think

Just did some quick search of the internet. In the not representative sample i also found that the amount of small arms carried seems to be linked to gun size. For the 3,7 cm Pak often the crew is seen with rifles. For the 5 cm Pak seldom and allmost never for the 7,5 cm Pak.
My guess is is there are several faktors at play. The larger guns are usually moved by vehicle. They are also more difficult to bring into position. It requires more labour. The ammo is larger and heavier.
Its also important to mention that a German AT platoon of WW2 has an MG section for close in defense.

I think it's both gun size and the distance from the enemy.

The bigger is the gun the further it is (usually) from the enemy and its infantry.

to change the subject slightly, didn't the netherlands airforce start to arm their pilots with MP9's?

According do the internet the Nethlands air force issued M9 to pilots flying anti ISIS mission.

No idea if they still issue the weapon or if they are issuing it more wide spread.

schnuersi said:

Looking at pictures with German troops from WW2 it mostly seem to depend how official the picture was. The staged, official propaganda pictures allways show soldiers in perfect uniform with rifle on the back. The snap shots taken during combat allways show very sloppy uniforms and no small arms nearby.

That's common in US photos, too.  But I did find a pic taken during the 1943 battle for Attu Island which shows M1 carbines on the backs of the gun crew.

schnuersi said:

Since there are vehicles everywhere there are GPMGs everywhere. In the past on pintle mounts nowadays often on RWS. So what is the point of issuing carbines or rifles? The PDW is absolutely sufficient to buy time until a GPMG or heavier weapon can chime in.

Hmm.  Replacing rifles and carbines with a PDW would permit elimination of 5.56x45 guns and ammo from the inventory in addition to those in 9x19 caliber, which would tremendously simplify logistics and training. 

Plus, it would reduce the soldier's weight burden, while also enabling a substantial increase in basic ammo load.  And being able to carry 300-400 rounds of ammo in 40-round magazines would enhance the ability to use the "area saturation" method to defeat Level IV body armor.  (Disregard the pistol in the pic.)

In addition, using a compact, lightweight PDW would better enable the infantry to evolve from the centuries-old paradigm of shooting bullets that put little holes in people and things, into a combat force that wields weapons of far greater destructive power.

Okay, you convinced me.  I'm in!