JJ typing, learning my Grey Knights has been the most difficult army than any other I've played. One thing I've learned about it is that I feel it matches the theme of the Imperium. As Suijin says: Imperium is a giant steamroller. Nothing can stop it. Worlds and other armies it crushes goes beneath its notice. Grey Knights are the same way.
“To achieve victory we must mass our forces at the hub of all power & movement. the enemy’s ‘center of gravity’” - von clausewitz
This is where every army excels. You take your hammer, entire army, and focus it on both immediate and long term plan(s) and you'll succeed. The hammer
is designed to work as one force. Enhancing the strengths of the units its working with. Some call this support. I prefer to say enhance. Example: Psyflemen is moving up with Purifiers. Enemy psyker casts a malediction power on the Purifiers. Instead of the normal -1 to the test it's -4 because of the Dreadnoughts Reinforced Aegis. Enhancing the negatives to the check from -1 to -4. That is a basic example. I'm sure you can think of several other examples.
Here's a question. What's the point of a hammer? To bludgeon something. Specifically to use weight, momentum and greater surface area to impose its will. A nail into an object, breaking concrete, smashing watermelons, the list goes on and on. In this instance a hammer is every unit in your army used to achieve your goal. Doesn't matter if the hammer is a Grey Knight army or Tau army. Ultimately it comes down to knowing how to use use the hammer.
|How not to use your army.|
What are the different ways you can use the hammer? In some situations you can use every shot in your army to take out specific models that directly affect the use of your hammer. Dive into the left or right flank, move up to the middle push enemy models where you want.
Of course the problem with a hammer is if its the only tool you have every problem looks like a nail. A hammer is really good at taking care of nails, when used correctly. Keep on task with your army. Don't get distracted. If you're looking to use the hammer to hold two corners of the table which contains three objectives use the army to fulfill that goal. Don't get sidetracked by boogieman or shiny objects. Here's an example. Say there are twenty Plague Bearers sitting on an objective on the different side of the table than your goal. Ignore them. Let the Plague Bearers keep that objective. Instead of two armies duking it out at 1850 pts the game is now 1850 vs 1670. In my opinion much better odds and far more favourable. That is my favourite type of game. Opponent is playing with a handicap and I'm able to utilize all of my points. Yes, in that scenario the Plague Bearers are fulfilling a purpose. Once I've accepted that it will take too much energy to remove those Plague Bearers, especially when that energy is better used to achieve my goal, that objective is no longer on the field. Effectively it becomes a hole in my vision.
This is where the scalpel differs. You don't have to use your entire army to achieve immediate or long term plans. The scalpel uses minute precise motions to achieve key tasks on the field. Such as sending a Wave Serpent to remove Tau Fire Warriors in area terrain off an objective. Or keeping jetbikes in reserves and moving them flat out onto an objective at the end of the game. These are little moves that don't need the entire army to achieve the desired goal.
Scalpels excise material from a body.
Using specific models to remove an armies efficiency by eliminating key elements of support. Example: Tau Broadsides taking out the opponents army high strength/low AP weapons. Again, I'm sure you've thought of a few more examples.
Scalpels are great for dissecting. Bit by bit removing the usefulness of an army. Usually this done by eliminate any immediate threats i.e. long range retaliation units. So you can shoot without any chance of getting shot in return. After those long range units are neutralized then the scalpel can move to its next priority. Perhaps incoming large bugs, fast attack units that can get in your grill extremely fast or scoring units, yada yada.
What's the point of a scalpel? To make surgical incisions. To do exactly what you want with minimal effort. Achieve victory with minimal necessary force. Something not mentioned when using a hammer is your opposing player's morale. Scalpels affect your opposing player's morale differently than a hammer. Instead of crushing defeat via a steamrolling going over their entire army. A scalpel slowly takes away the army's usefulness. Which, if done correctly, can be far more effective in placing despair squarely on his shoulders. Examples of scalpels: Sternguard with combi-meltas placed in specific parts of the field to take out each squads specific objective.
Problem with the scalpel is you may end up spending more points to destroy than the target unit is worth. Your scalpel may cost three times the points the unit it is designed to remove. That brings into question the effectiveness of the scalpel. Scalpels are great at taking care of something the rest of your army has a problem with. Example. Flamer unit to remove aforementioned Plague Bearers sitting on an objective.
Wrapping this up. I feel armies, not codexes, are either a hammer or a scalpel, few are both. It is my firm belief any army in the hands of a great general are both. Which means you need to put your army on the table a lot. You need to lose a lot. You need to adapt to your environment, what's on the table. You need to practice you're list, what units works and what doesn't. Ultimately it comes down to you playing and playing often to know when to utilize your army as the hammer or scalpel.