This is the whole reason I started playing KSP so many months ago, what I have worked toward, and what I have mastered.
Behold my greatest creation:
The Modular Cruiser D:
The Modular Cruiser D is a fully modular interplanetary capable armored weapons platform designed to be both mission kill resistant by subdividing and distributing mission critical components across the vessel and strategically upgradable and reusable by having dedicated reloadable ordinance docking ports as well as fuel cross-feed capable docking ports of both regular and junior sized, configured in such a way as to allow damaged modules to be replaced in any space based theater of operation with either newly boosted modules or by consolidating undamaged modules from two or more damaged Modular Cruiser Ds into one or more undamaged vessels.
THE HIGHLIGHTS:
Parts: 257 (includes full armament)
Total Mass: 120.19 tons
Total Fuel/Ox: 2,914/3,562 units
Total RCS: 600 units
Armament: 8x centerline forward facing direct fire Reloadable SRBs fired in 4 salvos; 6x manually guided anti-fighter missiles.
Armor: 2x Series 5 segregated, free-floating, replaceable "Clamshell" plate sections.
Fuel Module: A forward keel connects 8 fuel cells to compartmentalize damage; forward armor panel doubles as dock for reloadable SRBs.
Crew/Engine Module: The crew is protected by placing their compartment between the fuel module/SRB armament and battery/ rear keel, which connects 4 RCS cells with 5 Nuclear engines to compartmentalized damage.
THE CRAFT FILE IS HERE, AND INCLUDES THE BOOSTER (536 PARTS).
The operation of this craft is simple: Full throttle to orbit, gravity turn to 90 degrees at ~10-15km, and press the space bar to jettison empty stages. SRB salvos are fired by staging. Anti-fighter missiles must be manually undocked, select the jr. docking port farthest from the ship and control from there, and thrust it like a rocket using shift/ctrl/x into something else at high speed. Fuel/ammunition tenders/stations may come in another post.
The third image presented was took after I re-docked the cruiser to that floating clamshell armor section in the distance to prove that it could be done and document how much RCS it took. PRO TIP: fly the cruiser to the armor, not the armor to the cruiser, and DO NOT USE TIMEWARP; you do it by threading the docking port towers through the 1x6 meter gap between the engine armor cowls. I got it on the third try; it was the most thrilling maneuver I ever pulled off in KSP.
And now I shall end this post with an artsy picture of the Modular Cruiser D high over Kerbin, eclipsing the sun.