astern of the ship, although the sternward opening was much shallower. Since no known weapon could penetrate an impeller stress band, this meant no ship could fire at targets directly 'above' or 'below' it, but it also meant that fire directed at a ship from above or below was ineffective.
The sides of the impeller wedge, unlike its ends, could be closed by gravity sidewalls, a much weaker version of the impeller stress band. A warship's sidewalls were its first and primary line of defense, extremely difficult for missiles to penetrate (though there was an unending race between missiles with better sidewall penetrators and defensive designers' efforts to build ever tougher sidewalls) and invulnerable to even the most powerful energy weapons at ranges in excess of 400,000 to 500,000 kilometers (approximately forty percent of effective range against targets without sidewalls).
The fact that a ship could no more fire out through its impeller wedge than it could be fired upon also dictated the arrangement of its armament, most of which was grouped on the broadside, with a much weaker 'chase' armament arranged for fire ahead and astern. Chase armaments were intended to cover the blind spots in a vessel's broadside firing arcs, but they tended to be much lighter than broadside batteries because there was simply less hull volume in which to mount them.
Although no 'Holes' could exist in an impeller stress band, portals (known to naval spacers as 'gunports') could be opened in a vessel's sidewalls to permit unobstructed fire of its own weapons. In theory, gunports represented dangerous chinks in its defenses; in practice, the targets were too small and fleeting—they were 'open' only long enough for a shot to be fired through them—to be deliberately targeted. Nonetheless, it was not unheard of (though it was very rare) for a lucky shot to penetrate an open gunport.
Even a freak gunport hit, however, wasn't guaranteed to inflict damage. The maximum safe velocity in n- space was approximately .8 c for a ship with military-grade particle and radiation shielding, whereas merchantmen normally relied on much weaker—and less massive—shield generators, trading lower maximum speeds for greater cargo capacity. But speed wasn't the only reason military shielding was so much more powerful, for it was also used to fill the area between the sidewall and hull and could lessen or even negate the effect of a hit which managed to pierce the primary defense.
The constraints of the impeller drive and the fact that ships were designed for broadside fire also dictated their hull forms.
The nodes which generated the impeller wedge had to be very specifically located relative to the dimensions of a ship. In general, they had to lie within twelve to fifteen percent of the extreme ends of the vessel and well inside the maximum beam which the wedge allowed. Although there were a few idiosyncratic exceptions, this meant virtually all warships were flattened, 'hammer-headed' spindles, tapering to their smallest dimensions at their fore and aft impeller rings and then flaring back out to perhaps a quarter of their maximum beam. The fact that starships generated their own internal gravity allowed designers to orient 'up' and 'down' perpendicular to the long axis of the ship, which both permitted efficient usage of internal volume and gave renewed meaning to the ancient terms 'upper' and 'lower' decks.
Chase armaments had to be squeezed into the flared ends of the spindle, and there was little room, relatively speaking, into which to fit them. As a general rule, a light warships chasers might represent as much as a third of the power of its broadsides, but the proportion fell as the size of the ship grew. Truly enormous ships, like superdreadnoughts, might mount broadside weapons on as many as four or five separate decks, and their length was as much as seven or even eight times their maximum beam, which meant that each 'gundeck' offered twenty- five to thirty times the weapons volume available to their chasers.
The topsides and bottoms of warships were not armed, though a portion of those areas were used to mount various sensor and communication arrays. Some navies experimented with vertically mounted missile tubes in an effort to recoup that 'wasted space,' but with generally unsatisfactory results. A capital ship's impeller wedge might be as much as a hundred kilometers 'wide,' and no missile could activate its own impeller drive inside its mother ships drive perimeter lest its wedge impinge upon that of the launching ship. Since the interference between them would have vaporized the missile drive (and the rest of the missile with it), any missile's initial flight path had to be a straight line, directly away from the ship and ninety to a hundred kilometers in length, which no practical vertically-launched weapon could attain.
Broadside missile tubes incorporated powerful mass drivers to get the weapon outside the warship's wedge quickly, and, in theory, a vertical launcher could have used a mass driver with an internally curved path to throw a missile out a top-mounted tube at an angle which would clear the wedge. In practice, it was impossible to align the missile flight path precisely enough with a sidewall gunport, and the additional mass required by the longer, curved mass driver was prohibitive, and efforts to devise 'swim out' missiles which dispensed with mass drivers and relied on conventional thrusters for their initial acceleration proved universally disappointing.
All normal-space tactics and naval doctrine had evolved around the limitations and capabilities described above. Obviously, the bow or stern of a ship, which could not be protected by a sidewall, represented its most vulnerable aspect, and the ideal of virtually all normal-space tactics was to 'cross the enemy's T' and gain a 'down the throat' or 'up the kilt' shot with one's full broadside while he could reply only with his chase armament. Since both sides knew this, however, opportunities to cross the 'T' were rare even in single-ship duels and almost unheard of in fleet engagements.
The most common tactical situation was the broadside duel, in which both ships brought the full power of one broadside to bear upon the other. Even here, however, a canny captain never forgot the impenetrability of his impeller wedge. Whenever possible, he 'rolled ship' to take fire—especially missile fire—which he could not avoid against that powerful defense. At close range, lighter ships, which were much faster on the helm due to their lower masses, often resembled whirling dervishes as they spun back and forth in an effort to bring their own weapons to bear and then snap back around to deny their opponent a target for return fire.
Such energetic tactics, however, were less practical for fleet engagements. First, capital ships, which could mass up to 8,500,000 tons, were necessarily slower when it came to rolling ship, but, more important even than that, was the development of the formation known as 'the wall of battle.'
Since broadside fire was the only practical way to bring maximum fire to bear upon an enemy, admirals evolved the tactic of stacking their capital ships both vertically and in line at the smallest intervals their impeller wedge safety perimeters permitted. This produced the characteristic 'wall'—an often enormous formation, one ship wide, which might extend for thousands of kilometers vertically and ahead and astern along the fleet's base vector. This was scarcely a maneuverable formation, but at least it allowed maximum fire to be brought to bear.
Unfortunately, the tactical formalism fostered by the wall of battle also meant that major fleet engagements tended to be frustratingly indecisive unless one side was tied down by the need to defend a target which it simply could not abandon, like a populated star system. If one fleet took the worst of it and had no overriding strategic reason to fight to the death, its commander simply turned the units of his wall up on their sides, presenting only the roofs or floors of their wedges to the enemy, and then bent all his efforts on breaking away. An opponent who turned towards him to close the range and prevent him from disengaging (the only possible counter) might actually cross its own 'T', permitting his ships to roll back and fire their broadsides down the throat of the pursuing fleet with deadly effect.
On the rare occasions when warships clashed in hyper-space, the tactical environment was radically different. As a rule, starships in hyper tend to stay within the area of a grav wave, using their Warshawski sails to draw acceleration and deceleration from the wave, and normal impeller drives (including those of missiles) cannot be used within the area of a grav wave.
The Warshawski sail is essentially a highly modified and very powerful impeller stress band projected in the form of a disk at right angles to the hull, not as a wedge above and below it. The sail, which is just as impenetrable as an impeller wedge, extends for three hundred kilometers (as much as five hundred for really large vessels) in all directions. This not only makes chase armaments even more important but also deprives the warship of the protection of its wedge against fire from 'above' or 'below.' Indeed, it deprives a ship even of its sidewalls, for there are no roof and floor for the sidewall to stitch together.
One might expect admirals to avoid grav waves if forced to fight in hyper, but doing so is tantamount to breaking off the action. The reason is simple: a ship under Warshawski sail can pull almost ten times the acceleration it could under impeller drive. Withdrawing from the wave, then, allows a fleet which remains within it to run away with relative impunity.
A few navies have experimented with the idea of mounting the sidewall bubble generators used to generate 360° 'sidewalls' around fixed fortifications in their capital ships for use in hyper-space engagements, but
