Let it work;
For ’tis the sport to have the engineer
Hoist with his own petard; and it shall go hard
But I will delve one yard below their mines,
And blow them to the moon.

Hoist with his own petard
means killed by one’s own weapons.  Brewer explains that the petard was a thick iron engine, filled with gunpowder and fastened to gates for example to blow them up.  the danger was that the engineer  who fired the petard be blown up too.  The quotation is from Hamlet by William Shakespeare.

Leading from the rear was the preferred method of W.S. Gilbert’s Duke of Plaza-Toro.

File:William S. Gilbert (1878).jpg
W. S. Gilbert
Photo Credit Wikipedia http://en.wikipedia.org/wiki/File:William_S._Gilbert_(1878).jpg

If someone has another string to their bow they are borrowing an image from archers or bowmen.  If a bowstring broke and could not be replaces, they were no use in battle.  Nowadays the expression can mean someone has another means by which they might earn their livelihood.  Not to be confused with the string section of an orchestra using bows to play their instruments!

She looked daggers at me.
A dagger is a short sword.  Another similar expression is If looks could kill…

Cut and thrust sounds to me like a swordfight.  It is used to describe the competitive world we all live in.

A wounded soldier is often used to describe a child with a limb in plaster.

To go off at half cock comes from the action of firing a gun.  A gun has to be cocked before the trigger will fire a bullet.  If this is not done properly, the bullet does not get far.  The expression is used for anything which is launched too soon and does not succeed for that reason.

Going great guns means doing well.  Cannons were great (big) guns.

Lock, stock and barrel describes the whole of a musket.  So this has become a metaphor for complete.

A council of war a meeting to discuss strategy, which has been adopted by civilians.

It’ll pass muster.  Muster means gather together.  Troops are gathered together for inspection.  This phrase is used for anything which is satisfactory.

We’re the advance party.  A few people arriving ahead of a larger group may say this.  It describes a small group going on ahead to prepare for the arrival of the rest or scouts going ahead to spy out the land.  Joshua and Caleb were good scouts.   Numbers 13: 16-33

She was up in arms.  She objected strongly and even prepared to fight; on the warpath means much the same.

Synchronise watches!
 Before the railways all the towns in Britain had their own time.  Not all watches keep perfect time.  If there is going to be a rendezvous setting all the watches to the same time will help.

A guard of honour is a double line of uniformed personnel.  A bride and groom may walk between the two lines, when it is a mark of respect to them.

Beyond the call of duty means over and above one’s job description.

He met his Waterloo means he was defeated.  Another blogger has posted an excellent piece about the background to this phrase.  I urge you to click on the link and read it.