by David Weber
MARK III BOLO (2018):
A near contemporary of Mark II, the Mark III was actually designed as a “heavy” (300 metric tons) companion vehicle. The Mark III’s single 150mm main gun (which was not turreted and had only a 20 degree traverse) was backed by an 8-gun infinite repeater battery, a heavy indirect fire support capability (four 155mm howitzers and a light VLS missile system), and an upgraded anti-missile armament. Unlike the Mark II, the Mark III carried only a single fossil-fueled power plant, strictly for backup use; power was normally drawn from heavy banks of ionic batteries, and the Mark III was the first Bolo designed from the outset to use solar film recharging. The vehicle also carried a marginally better sensor suite and a thicker durachrome hull (20 millimeter) which could be pierced at pointblank range (250 meters or less) by a 90 degree hit with the 140mm or 150mm DSFSLRP round; otherwise, it was effectively immune to anything short of a contact nuclear explosion. The Mark III was designed for a two-man crew with the second crewman serving as electronics officer (EW, sensors, etc.), but could be crewed by a single experienced operator in a pinch. The last Pre-Collapse Bolo, it was the first Bolo with multiple tread systems-inner and outer-with an independent power train for the inner pair, but maximum speed fell to 50 kph (road), 25 kph (cross-country).
MARK IV BOLO (2116):
The first Post-Collapse Bolo picked up where the Mark II left off. The Mark IV had a much improved sensor suite and carried a main armament of one 165mm railgun, backed by six infinite repeater railguns (20mm). The Mark IV was the first Bolo to use energy weapons (laser clusters) to supplement projectile weapons in the point defense role and was fitted with seventy-five vertical launch system missile cells in its after decking, capable of accepting indirect fire support or SAM loads but without onboard reloads. Powered as Mark III, but with improved solar film. (It was no longer necessary to stop and deploy acres of film; the Mark IV could recharge on the move in average daylight conditions.) The Mark IV’s durachrome hull was thicker (30 millimeter), yet weight dropped to 210 tons in the Model B, with a maximum speed of 60 kph (road) and 30 kph (cross-country). Missile load and sensor upgrades continued to drive up the tonnage of successive models, however; by the end of its active life, the Mark IV did carry onboard missile reloads and weight had risen to over 340 tons while maximum road speed fell to 40 kph, with very limited rough terrain capability. (The Mark IV, Model H, for instance, could get through almost anything, but its suspension and power train weren’t up to crossing rough terrain at any kind of speed.)
MARK V BOLO (2160):
The first member of a family of specialists with roughly comparable onboard computer support but different weapons fits and functions. The Mark V was the first so-called “deep-wader”—that is, it no longer required bridging support, as it was designed to cross water barriers (including lakes and even small seas) by submerging and driving across their bottoms-and this capability became standard with all subsequent marks of Bolo. Power demands continued to grow, surpassing levels which even ionic battery technology could meet, and the Mark V was the first Bolo to use an onboard fission power plant. The growing size and weight of later models of the Mark IV had led to efforts to diversify design in the immediately subsequent marks, and the Mark V was the “general battle tank,” fitted with a heavy caliber railgun (190mm) for main armament, supported by twin lateral batteries of six 60mm “gatling-style” infinite repeaters using spent uranium slugs and lighter gatlings and laser clusters for point defense. The laser clusters’ anti-personnel function was limited, and the Mark V also saw the first use of multishot anti-personnel flechette/HE clusters, which became standard on all subsequent Bolos. Missile capacity was severely down-sized and restricted to SAMs as part of the drive to hold down weight. The Mark V had a one-man crew, a battle weight of approximately 198 metric tons, and a maximum speed of 50 kph (cross-country) to 80 kph (road).
MARK VI BOLO (2162):
The Mark VI was the direct descendent of the Mark III “mobile firebase” concept. It had the same power plant and computer support as the Mark V, but the Mark VI’s “main battery” was its missile load, which was configured for maximum flexibility. No railgun main armament was mounted, but the 60mm infinite repeaters were upgraded to seven guns per side, and a heavier point defense battery intended to provide cover for other friendly units and to protect the Bolo itself when operating in counter-battery mode was fitted. One-man crew; 238 tons; speed roughly comparable to the Mark V’s.
MARK VII BOLO (2163):
The Mark VII was a “heavy” Bolo, whose introduction inspired the first use-though still unofficially-of the term “siege unit.” It had the same electronics fit as Marks V and VI, but its main direct-fire armament was one 200mm railgun backed by fourteen heavier (75mm) infinite repeaters. The Mark VII’s heavy missile load was biased towards the bombardment function, but it was equally capable of operating SAMs in the area defense role. This vehicle has a very heavy layered durachrome war hull (120 millimeter) and required a two-man crew, rather than the Mark V’s and VI’s one-man crew, but in the VII/B the second crewman served solely to control the indirect fire armament. In later models, the second position was upgraded to a dedicated air-defense/missile intercept function. Weight was approximately 348 tons in the Model B, with a maximum road speed of 40 kph and a maximum cross-country speed of 30 kph. (The Mark VII was never very fast, but its sheer mass meant most terrain features tended to crumple when it hit them and so did not slow it as severely.)
MARK VIII BOLO (2209):
The Mark VIII was the next-generation “main battle” (or “standard”) Bolo. Main armament remained a railgun, though muzzle velocity increased still further and projectile size fell slightly (to 170mm), but this Bolo marked the first appearance of energy-weapon (laser) infinite repeaters. (By the time of the Mark VIII, any Bolo’s secondary battery had come to be referred to as “infinite repeaters” whether or not they fired actual projectiles.) Although the new laser infinite repeaters were actually marginally less effective than the last-generation railgun infinite repeaters on an energy-transfer-per-hit basis, mass per weapon fell, and the shift meant magazine capacity for the secondary battery was no longer a design factor. Missile capability was limited to the SAM and point defense role, but the Mark VIII received four hull-mounted 150mm rapid fire howitzers to compensate. The VIII/B was fission-powered, with solar charge backup capability, a one-man crew, and a weight of approximately 225 tons. Improved power train and suspension permitted a sustained road speed of 65 kph and short-range “sprint” speeds of up to 85 kph, but maneuverability at high speed was poor.
MARK IX BOLO (2209):
The Mark IX was the next generation “siege” unit, introduced simultaneously with the Mark VIII as companion vehicle. The main battery railgun was suppressed in favor of additional missile power and four high-trajectory 180mm howitzers in two back-to-back twin turrets. Further improvements in electronics allowed the Mark IX, unlike the Mark VII, to be crewed by one man. Weight was approximately 400 tons, and maximum road speed for the IX/B was 57 kph.
MARK X BOLO (2235):
The Mark X saw the first appearance of an energy main armament (laser cannon) in a Bolo. As with the laser infinite repeaters of the Mark VIII and IX, the new system was actually less destructive than the one it replaced on a per-hit basis, but it required no magazine space. The Mark X was fission-powered and carried laser infinite repeaters, and approximately 1/3 of the preceding Mark IX’s gatling closein anti-missile and anti-personnel weapons were replaced with multibarreled flechette-firing railguns in independent housings. The Mark X carried only self-defense missiles and no high-trajectory indirect fire weapons and required a one-man crew. Later models of this mark had sufficient computer capability and flexibility to begin use of pre-loaded computerized battle plans, requiring human intervention only when unanticipated tactical situations exceeded the parameters of the battle plan. The Mark X, Model B’s battle weight was 350 tons, with a maximum road speed 70 kph
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MARK XI BOLO (2235):
The Mark XI was essentially a backup, designed to cover the possibility that the Mark X’s laser main armament might prove impractical in service. Main armament was one 18cm railgun firing depleted uranium long-rod penetrators in the anti-armor role and a wide range of cluster, incendiary, chemical, and fuel-air rounds against unarmored targets. Otherwise, the Mark XI was identical to the Mark X. This vehicle remained in service longer than might otherwise have been anticipated because the projectile-firing capability of its main gun proved extremely popular with tacticians.
MARK XII BOLO (2240):
This was the first true “continental siege unit,” designed for strategic indirect fire with VLS cells capable of handling missiles with intercontinental range. The Mark XII was capable of MIRVed FROB attacks and of engaging orbital targets with hyper-velocity surface-to-space missiles. Main anti-armor armament was deleted, but the Mark XII was equipped with extremely capable anti-air/anti-missile defenses (in effect, it was an area defense system, as well as a bombardment unit). The vehicle was normally mated with a BAU (Bolo Ammunition Unit), a Mark XII with all offensive armament deleted to provide magazine space for multiple load-outs for the Mark XII’s missile batteries. Although the Mark XII continued to carry a one-man crew, it was primarily designed for pre-loaded computerized battle plans. Weight was 500 tons, with a road speed 50 kph.
MARK XIII BOLO (2247):
The Mark XIII was essentially a Mark XII with main anti-armor armament restored. Although the main gun ate up almost 25 percent of the tonnage dedicated to magazine space in the Mark XIII, the Mark XIII’s bombardment capability actually slightly exceeded that of the Mark XII with only minimal overall weight increases. This was made possible largely through improvements in fission technology (allowing a smaller power plant) and the first use of a flintsteel inner war hull under a much thinner durachrome sheath. The Mark XIII/B’s weight of 565 tons held fairly constant in all models of the mark. Road speed was 50 kph in the XIII/B, rising to 75 in late-series models as suspension and power train improvements became available.
MARK XIV BOLO (2307):
The Mark XIV replaced the never entirely satisfactory laser “main gun” of earlier marks with the far more destructive “Hellbore” plasmagun. This 25cm weapon, originally designed for the Concordiat Navy’s Magyar-class battlecruiser’s main batteries, had a half-megaton/second energy output and, unlike the earlier Bolo laser cannon, was a marked improvement over any kinetic weapon of equivalent mass. In other respects, the Mark XIV was a “standard” reversion to a generalist design, made possible by advances in mag-bottle technology (which finally made fusion power a practical alternative to fission in Bolo design) and acceptance of a lighter indirect fire capability. Anti-missile defenses were now sufficient to render strategic bombardment impractical, so indirect fire was limited to tactical and theater applications. This permitted the use of smaller missiles which, in turn, allowed an increased magazine capacity without weight penalties. Even so, the Mark XIV/B was 28 percent heavier than the Mark XIII/K it replaced, although further power train and suspension upgrades prevented any loss of maneuverability or cross-country performance. Gradual improvements in sensor fits and fire control systems kept this mark in front-line service for approximately 90 years. Tactically, primary reliance now rested firmly upon pre-loaded computerized battle plans, but a single human crewman was routinely carried to respond to unanticipated threats. The Mark XIV/B’s weight was 728 tons (rising to 900 in late-series models), and road speed hovered between 60 and 75 kph over the life of the mark.
MARK XV/BM BOLO (Resartus) (2396):
A quantum leap in Bolo technology, the Mark XV was the standardbearer of the Concordiat during humanity’s greatest wave of interstellar expansion. Very few non-human species encountered during this period could match the Mark XV’s capabilities; none could exceed them. This was the first Bolo which did not require an onboard human crewman, due to advances in cybernetics and secure communication links (first short-range subspace com capabilities), which permitted increasingly sophisticated computerized pre-battle planning coupled with unjammable remote human control to correct for unanticipated problems. Main armament was one 25cm Hellbore with line-of-sight capability, backed by laser cluster “gatling” infinite repeaters (total of fourteen in the Model B) and four 20cm howitzers in individual secondary turrets. The 25cm Hellbore remained incapable of engaging orbital targets from planets with atmosphere due to as yet unsolved attenuation and dissipation problems with the weapon’s plasma bolt “packaging,” but there were few planetary targets with which it could not deal. Tactical and theater bombardment capability was roughly equivalent to the Mark XIV’s, but the Mark XV had no strategic bombardment capability. The Mark XV’s six track systems each had an independent power train, and the vehicle carried both primary and secondary fusion plants. Cybernetics were divided between two totally independent command centers as protection against battle damage, and durachrome was wholly abandoned in favor of a much tougher flintsteel war hull. Early models of this mark saw the last use of anti-kinetic reactive armor. Major improvements in suspension were required to deal with unparalleled battle weights (1,500 tons in the Model B, rising to over 3,000 in the Model M), but road speed held constant at approximately 65 kph (with brief “sprint” capability of over 80 kph) over the life of this mark, although the “lightweight” Mark XV, Model L, EW platform, at barely 1,100 tons, was 37 percent faster. Cross-country speed was equivalent to road speed except in very rugged terrain. This mark enjoyed a very long, very stable evolutionary history (mainly because the Concordiat didn’t run into anything a Mark XV couldn’t handle).
MARK XV/R BOLO (Horrendous) (2626):
The Model R was the final variant of the Mark XV. Main armament was upgraded to one 50cm Hellbore (which, unlike earlier models’ weapons, could engage spacecraft in low orbit even from within a planetary atmosphere), and ablative armor appliques were fitted over the Model R’s flintsteel war hull in light of increases in infantry and light-vehicle energy weaponry. The preceding Model Q had seen vastly upgraded EW capabilities and the first appearance of heuristic cybernetics designed to run continuous analyses of pre-loaded battle plans against actual battle conditions in order to suggest improvements to its distant human commander. Under express human pre-battle authorization, the Mark XV/Q and /R were capable of reconfiguring their battle plans on the move without further human input. Although not self-directed, the final models of the Mark XV gave a very good impersonation of a war machine which was. Weights climbed sharply-the Mark XV/R reached 5,000 tons-but maximum road speed held fairly constant at 65-70 kph, despite weight increases.
MARK XVI BOLO (Retarius) (2650):
The increasing size of the Mark XV led to a fresh attempt at specialized design, and the Mark XVI was, in effect, a “light” Mark XV. Main armament remained a 50cm Hellbore, but the infinite repeater batteries were reduced to a total of eight weapons and the howitzer armament was deleted. (As partial compensation, the Mark XVI replaced its laser infinite repeaters with ion-bolt projectors, with much greater ability to penetrate ablative armor, and received a six-gun battery of short-range breech-loading 20cm mortars to augment its anti-personnel clusters.) A complete ablative outer hull was adopted to replace previous appliques, and cybernetics were equivalent to those of Mark XV/R. Weight fell to 3,600 tons, and road speed rose to 90 kph with short duration “sprints” of up to 100 kph possible. The Mark XVI formed the “light regiments” of the original Dinochrome Brigade.
MARK XVII BOLO (Implacable) (2650):
Introduced simultaneously with the Mark XVI, the Mark XVII was the “heavy” version of the same basic weapon system. Main armament was upgraded from a 50cm Hellbore to a 60cm weapon, and the ion-bolt infinite repeaters were increased to a total of fifteen (six each in two lateral batteries with a three-gun frontal battery in the glacis). The Mark XVI’s mortars were deleted in favor of six 25cm howitzers and an increased
missile armament. Weight increased to 6,500 tons, and maximum road speed dropped to 75 kph. The Mark XVII formed the “heavy regiments” of the original Dinochrome Brigade.
MARK XVIII BOLO (Gladius) (2672):
While the Mark XVI was more agile and easier to deploy than the Mark XVII, it proved less popular in combat than its companion mark because of its lighter offensive power. The Mark XVIII replaced both the XVI and XVII in relatively short order as the new “standard” Bolo in an attempt to combine the best features of both its immediate predecessors. As usual, the new vehicle went up in size and weight (late-model Mark XVIIIs approached 10,000 tons), and space-to-ground deployment became a problem. Main armament was the Mark XVII’s 60cm Hellbore, but the infinite repeaters were reduced to twelve with the deletion of the bow battery (which had been found to compromise the structural integrity of the glacis plate). The Mark XVIII adopted a “sandwiched” hull: an outer ablative hull, then a thin hull of early-generation duralloy, and finally the flintsteel main war hull. The Mark XVIII also added a third fusion plant, which, with additional improvements in fire control, plasma containment technology, and weapons power, permitted its Hellbore to engage spacecraft even in medium orbit. The Mark XVIII formed the first “general purpose” regiments of the Dinochrome Brigade and, in successive models, remained first-line Concordiat equipment for over a century. Maximum road speed fell to 70 kph and maximum “sprint” speed fell to only 80 kph, but except in the roughest terrain, a Mark XVIII was as fast cross-country as on a road. (Of course, for vehicles as large and heavy as a Bolo, “roads” had long since become a purely relative concept.)