unitReady

Keep in mind that

• dead units are unitReady
• it takes a while until it get's known to group members that a unit is not alive anymore, which leads to
• the current leader of a group might be actually dead (until another group member takes command). Why this is important? I'll give you an example: if you're using unitReady as a condition inside one of your fsm to advance whatever the fsm/group is doing, you really might wanna check that this unit is actually still alive. Otherwise you might end up with really fast and nasty loops in your FSM, eventually accompanied by a stream of radio commands that will last until finally a living leader is in command again.. and that could take a while... nasty, I tell you :)

Regarding vehicles, there is only one single unit (from the vehicle crew) whose unitReady-status is affected by giving that vehicle (or that unit) commands. While it is the driver unit for a truck, it is the gunner unit for a mg-jeep or the commander for a tank. Generally it is always the unit "in control" of the vehicle. (because it is only that unit, that is seen as "full unit" to the "outside world". Only he can be adressed with commands.)

In consequence you can't just send vehicles around and check if they've arrived with something like:

waitUntil { unitReady driver _vehicle }; // don't do this!

Because it is not guaranteed that the driver is in command of the vehicle and only that unit will have its unitReady status affected.

So in conclusion, if you need to check if a vehicle is ready, try something like this:

_vehicleReady = {
    private ["_veh", "_ready"];
    _veh = _this;
    _ready = true;
    {
        if (not isNull _x) then
        {
            _ready = _ready && (unitReady _x);
        };
    } forEach [
        commander _veh,
        gunner _veh,
        driver _veh
    ];
    _ready
};

To check readiness of a vehicle, don't check its crew, driver, gunner, commander, etc., but the vehicle itself, e.g.:

unitReady _yourVehicle;

Only tested 11/21/2015 by me with A2 1.63.131129 and A3 1.52.132676 but possibly true since 1964. :P