Yes, the subterranean option is a relatively new one, made feasible by recent technologies and new materials. It's still relatively primitive and limited compared to the other modern theaters of war, but it's largely immune to weather manipulation, practical air and space surveillance, and even direct hits with nuclear weapons, if desired (you just choose your operating depth). Too, as many nations now have substantial underground power/telecommunications/transit and even housing systems-- and those systems are often heavily protected from all directions BUT subterranean, weapons which can penetrate and damage/destroy those systems can be significant in time of war.
Basically we're talking underground robotic mini-subs/tractors here, which can tunnel at respectable speeds over respectable distances to attack/sabotage/spy on enemies from beneath. It's suspected that there's a handful of advanced models during this period capable of actually penetrating the mantle itself to achieve global or near global range at speeds approaching those of sea-going naval vessels from the late 20th century (however, mantle penetration/navigation is problematic for several reasons, and therefore a very limited practice at this time).
More typically however, such devices are limited to being transported via air, sea, or land by other means, to a deployment point within 50 miles or less of an enemy target, and expected to reach the target within days or weeks after that. Once there the subterranean device may simply detonate an onboard explosive, or perform other, more sophistocated duties.
One relatively new and scary weapon in the modern military arsenal now is man-made earthquakes and tidal waves (as well as countermeasures). Although crude and unpredictable versions of these were available militarily as far back as 150 years ago, advances in nuclear weapons technology, computers, and geological knowledge have now made it downright practical for purposes of war, in many instances. No longer do perpetrators require convenient vertical drilling access to plant nukes for quake initiation; for horizontal drilling and placement over hundreds of miles is now possible. But even that is often unnecessary, as with proper placement and equipment initiating missiles may simply be fired into the ground from combat aircraft, or bombs placed via subterranean tanks/crawlers. In some instances it is even possible to simply project concentrated solar powered microwave beams from satellites into certain mineral deposits or groundwater reservoirs to induce an eventual quake for military or other purposes. There turns out to be a startlingly wide array of choices for triggering earthquakes and tidal waves (at least in certain areas of the globe, if not all). For maximum effectiveness (and minimum uncertainty), comprehensive geological surveys of target areas and state-of-the-art computing hardware/software is required.
The possibilities of tsunami generating bombs were secretly tested by USAmerica near New Zealand during World War II.
-- EXPERIMENTAL BOMB TO CREATE HUGE TIDAL WAVE WAS TESTED IN 1944, Independent UK News, found on or about 9-27-99
But not all the news on this is bad; for the same technologies are suitable for countermeasures too, and are often utilized today in certain places (like the Pacific Rim) to minimize the risks of natural earthquakes/tidal waves. Of course, minimizing natural or artificial quakes/tidal waves with your own anti-quakes/waves is riskier and more difficult to accomplish than straightforward quake/wave creation for simple purposes of destruction. There is also the increasing uncertainty involved for all participants in such actions, as more and more independent entities gain their own means of theoretically instigating or reducing quakes/tidal waves, not only for military and disaster control purposes, but others. Chaos theory points to an eventual calamity from the use of these technologies by many parties in unilateral ways....
Today, even the human beings manning control and communications stations far from any actual combat tend to be cyborgs-- part biological, part machine.
Why? Because their positions to the rear often are little safer than positions at the front-- especially when their robotic forces are deployed against an enemy comparable to themselves in military prowess. Such command and control stations must by necessity be small and widely dispersed as well, to make them less conspicuous targets. So typically there's few human personnel onsite to repell a direct attack. In many cases an entire station of this sort will consist of but a single soldier in an updated version of the 'dream-mare' suits used in the 2060s, directing a remote force of robots in an attack or reconnaisance mission. The cyborg will be virtually invisible with on-person technologies, and enjoy additional active camouflage help from orbiting satellites and robotic aircraft. The soldier might not even physically move for days at a time under some circumstances. But if he/she does decide to move, they can fly at supersonic speeds, launch and land like a VTOL, and travel submerged undersea as well. If flight capacities are damaged or constrained, they can make short 'hops' of approximately a quarter-mile at a time (or less). The cyborg will usually enjoy a personal escort of one to two dozen escort robots, of varying configurations and capabilities. The basic mission of this entourage is to extend the cyborg's sensor net, and keep any attacking force busy while the cyborg performs his/her primary mission and/or escapes.
The cyborg also enjoys his/her own personal PestX cloud and/or carpet, to do with as they will. Such a body may divide into smaller forms to take on different jobs, but it's most powerful and versatile in unified form (the smaller a subdivided cloud portion, the 'dumber' it is). In some cases one or more of the cyborg's robotic escorts may also possess a PestX cloud/carpet. The PestX remains one of the most formidable general purpose weapons systems on the planet even now, although almost all standard military strategies and tactics have assumed the presence of PestX, and taken appropriate counter-measures as a matter of course for many decades now. For example, sea-based military platforms and vessels often possess one or more PestX clouds/carpets themselves, and some do little more than host hundreds or thousands of such clouds/carpets for weaponry, as these systems are replacing some previous forms of military aircraft, boats, and submarines.
The cyborg and its escort robots in fact have begun to merge with their PestX clouds/carpets in some ways, by this date. I.e., their outer skins may in some cases transform themselves in a matter of seconds or minutes into various contingency forms, such as armor with increased resistance to radiation, or to mirrored surfaces for protection against lasers, or foam up into insulation suitable for absorbing sonics or radar beams or to resist extreme temperatures. In some cases highly specialized tools may form out of certain skin areas, to aid with a job. In other words, military cyborg outer shells/armor may sometimes act like an intelligent fluid, capable of phase-changing into a variety of thicknesses, densities, materials, shapes, and degrees of hardness/flexibility.
Today camouflage/invisibility ranks among the highest priorities in military technologies. Unfortunately, they are increasingly difficult to attain. Therefore strategies are including 'flooding' tactics, whereby enemies are (hopefully) drowned with more complex information than their systems can cope with during critical combat events. Military assets try to be 'imposters', posing as an enemy's own assets on enemy screens. 'Deep cover' assets are sometimes installed in enemy territory months or years before probable hostilities take place, to provide surprises in combat (yes, this means powers are often secretly placing weapons systems within friendly countries during peacetime to prepare for possible war later). Such covert emplacements often become obsolete before they can be used however, therefore spurring their replacement with newer stations at periodic intervals or opportunities. Not all such secret installations may be retrieved however, and so often lie hidden somewhere until chance discovery by civilians or commercial concerns, at which time they prove an embaressment to their creators-- IF their creators can be successfully determined, which often they cannot. Enormous problems arise from the 'black' nature of various 'invisible' weapons systems, due to the minimal documentation performed in order to reduce their vulnerability to cyberwar/espionage (the enemy discovering their existence via cracking databases). A great many secret weapons are simply LOST in this way, with a resulting bleeding of military budgets.
Inert/dormant PestX clouds/carpets are increasingly being deployed as covert weapons systems due to their war flexibility and difficulty to detect while dormant. When called upon for war, these systems may suddenly seem to appear from nowhere right at enemy headquarters, or at a head of state's residence.
The increasing awareness that deadly inert PestX clouds/carpets may be anywhere doesn't do a lot to increase feelings of security on the parts of many civilians during this time. The biggest effect of this may be yet another source of annoyance with the old geopolitical entities.
Most truly important battles now are usually fought mostly at sea, under it, or in space or cyberspace.
The ever-widening technological options available to everyone, plus increasing wealth/productivity of average citizens and ironically relative decline in power, wealth, and efficiency of most old geopolitical governments, is turning the world upside down today. As the concentration of ever greater proportions of government resources into an ever smaller variety of technologies increases, the potential for mistakes (even just by degree) compared to those of a diverse mass population makes it ever easier for smaller organizations and even individuals to 'leapfrog' government resources and technologies at an ever faster pace.
Increasingly the old geopoliticals are losing prestige and real power to entirely new groups and associations and ideas forming spontaneously among the world population, and nourished by the net. The old geopoliticals are increasingly perceived as something akin to the "Keystone Cops" of silent films a couple centuries before, despite the fact they still possess some formidable weapons and other tools at their disposal. Indeed, the fact that they are perceived this way might offer you some idea of the state of readily available consumer technologies today....
There are LOTS of mercenaries now, using mixes of old and new military technologies, as well as improvisations of other ad hoc choices. There's also a great many Vigilantes/Zee-roes of varying degrees. Vigilante/Zee-ro organizations exist as well, but in a chaotic, complex dance of everchanging allegiances and membership requirements that often defy the best efforts of outsiders to decipher or keep up with.
Most other military technology of this period consists of little more than linear/incremental developments/improvements upon technologies available in the 2060s.