Introduction
I'll start by assuming you've read the docs of the current version of host.exe (3.22.012) and that you're familiar with the concepts of the 'Ship Building Queue' and the '500 Ship Limit'. If you're not, you should first read the docs that come with Host.exe.

In this article I'll try to share my little bit of knowledge about the Ship Queue with you. First I'll give a description of the building and cloning of ships and how it works precisely. I'll introduce the Priority Build Points, and after that I'll describe the odd behaviour of the Ship Queue. Finally I'll give you ten tips of how to use your new knowledge of the queue to the uppermost level of devastation...!

Ship Building and the Mission Ordering
Before anything else you'll have to know where exactly the building of new ships happens between all other commands processed by host.exe. The following is taken from the most recent version of Infolist, v 3.1 (1).

    Auxhost 1
    ....
    Ion Storms
    ....
    Starbase Fix/Recycle functions
    New ship building                  (1)
    Cloning starships
    ** Federation Super Refit mission **
    Ship surrendering
    ...
    Movement
    Intercept missions
    Glory Devices
    ...
    Star Base missions
    Colonize missions
    COMBAT! Ship to Ship
    COMBAT! Ship to Planet
    ...
    Planetary production
    New ship building                  (2)
    ....
    Auxhost 2
    ....

As you can see there are two moments where new ships are build. I've numbered them phase 1 and phase 2. What's the difference between those two phases? Well, phase 1 is the same as the 'regular' building phase of host 3.1x. Phase 2 has been added since the coming of host 3.2x (and the Ship Queue). Hmmmm, what does this exactly mean?

The difference between Phase 1....
When there is a free ship slot when the host enters phase one, a ship will be build.
All ships will be build in phase one until the game hits the 500 ship limit. Simple as that. When there are still free ship slots left after all queued ships have been build in phase one, ships can be cloned. When all queued ships have been build in the first phase the second build phase won't be used.

.... and Phase 2
In between phase 1 and phase 2 there is the COMBAT phase: ships will be destroyed, and there will be some free ship slots again. When there are still queued ships left host.exe will build those in phase 2.
After the ship limit most ships will be build in the second phase. This means that in most cases YOUR SHIPS WILL BE BUILD AFTER COMBAT WHEN THE SHIP LIMIT HAS BEEN REACHED, and not before..... (This could be important when your starbase is under attack...)

See also note (2).

Free Ship Slots after the Ship Limit
To make the difference between phase 1 and 2 I'll give some examples of how ship slots are freed and when they are used. The game has reached the ship limit. (Or else phase 2 wouldn't be used, remember?)
Take a look at the extract of the Mission Ordering of the Infolist above, and examine this:

• When a ship is destroyed in a ship to ship battle, a new ship with the same ID as the destroyed ship will be build in phase 2. (Combat happens between phase 1 and phase 2.)
  
• When a ship is recycled, a new ship with the same ID as the recycled ship will be build in phase 1. (Recycling happens before building phase 1.)
  
• When a ship is colonised, a new ship with the same ID will be built in phase 2. (Colonising happens after movement.)
• When a Glory Device sets of, a new ship with the same ID as the exploded ship will be build in... right: phase 2.

• recycling ships at starbases;
• ships exploding in Ion Storms;
• every event that destroy ships in Auxhost 1;
• idem Auxhost 2.

• ships exploding in minefields;
• the Colonise ship mission;
• Glory Devices;
• Combat.

Cloning Ships
You can clone a ship before the ship limit, and you can't clone a ship after the ship limit has been reached. Why? Simple: Cloning happens right after the first building phase - and before the ship limit there are still free ship slots when the host processes the Cloning phase. After the 500 ship limit all free slots - if there were any - will have been filled by queued ships in the first building phase.
If you want to clone a ship after the 500 ship limit you will have to take care that there are enough free ship slots in the first building phase for all queued ships and your clone. You could do this by doing one or more of the following:

1. cancelling/withdrawing of all queued ships on most (if not all) starbases;
2. freeing lots of ship slots before phase 1 by recycling ships;
3. using KillRace.exe.

Priority Build Points
I'll introduce the use of Priority Build Points (PBPs) here. If you don't know what they are, read the docs. In general you earn PBPs when you are the player freeing a ship slot.

You will get PBPs for:

• Destroying an enemy ship in a ship vs. ship combat (1 PBP for every 100 kt of enemy hull mass, rounded up);
• Capturing an enemy ship in a ship vs. ship combat (1 PBP)
  [host 3.22.008 and older];
• Recycling your ship (1 PBP);
• Colonising your ship (1 PBP);
• Setting of your Glory Device (1 PBP);
• Destroying an enemy ship using Glory Devices (1 PBP for every 100 kt of enemy hull mass, rounded up).

You won't get any PBP for:

• Surrendering a ship at a starbase (without fuel or with matching Friendly Codes).
• Giving ships away using the 'gsN' Friendly Codes.
• Destroying an enemy ship in a ship vs. planet/starbase combat.
• Destroying an enemy ship in a minefield.

Using Priority Points
You'll start using your Priority Points when you've got more than 20 PBPs. (This holds true for everything mentioned below.)
So if you've got 21 or more points and there are free ship slots you will use your priority points. This means that before the game hits the 500 ship limit you can't accumulate priority points with the intention to collect an enormous stockpile of points and use them after the ship limit. That won't work.

The rules for using PBPs are simple: the player with the most PBPs will get the first free ship slot. When that player has his new ship, his PBPs are recalculated. Then again the player with the most PBPs will get the next free ship slot. This could be the same player, but it could be another. Etc.

In older versions of host.exe, these rules could result in two nasty situations:

1. When the player with the most PBPs doesn't use them, no other player can use his PBPs. Of course ships will be build, but without using priority points. This can be extremely annoying when this player is a Computer Player. This is fixed in host v3.22.006: If the player with the most PBPs doesn't build any ships, the player with the second to most (but still more than 20) PBPs will get the next free ship slot etc.
2. The Ship Queue could skip one of the queued ships on your starbases. This is fixed in host v 3.22.11 - the regular queue (i.e. that queue that won't use PBPs) isn't influenced by the other, PBP using queue.

Priority Build Friendly Codes
As of host v3.22.011, Tim has introduced the Priority Build Friendly Codes (PBFC). These codes are planetary friendly codes and regulate the Priority Build Queue only. The codes are 'PB1', 'PB2' .... to 'PB9'. They work very simple: if you have more than 20 PBPs and there is a ship slot free, a ship will be build on the starbase that carries the lowest PBFC. This build will cost you PBPs. Additional:

• This is valid for both build phases.
• The 'PB0' friendly code doesn't work.
• When there are duplicate PBFCs (for example when you have set the FC 'PB1' on two starbases) the ship will be build on your starbase with the lower ID.
• A PBFC on a planet (without a starbase) will be ignored.
• If you don't use these Friendly Codes (STUPID! STUPID! STUPID!) your priority builds will happen at your first ships in the Regular Queue.

Two Queues
Since host v3.22.011 there are two queues: the Regular Build queue that keeps on cycling from base ID #1 to base ID #500, and the Priority Queue that jumps to the starbases where you've set the PB Friendly Codes.