Executive summary: After five years of war against the Saudi-led coalition and its allies, Yemen’s Houthi rebels remain defiant and are once again on the offensive. The Houthis’ keen understanding and consistent application of the algebra of insurgency are fundamental to their martial success in Yemen. Ironically, the greatest threat to the Houthi leadership may be peace. Peace will bring internal tensions within the Houthi leadership and growing discontent among the Yemeni people to the fore.
Underestimating or having contempt for an enemy, argues Lao Tzu, is among the costliest mistakes a commander can make.  This alone has led to more defeats than any other miscalculation. Conversely, underestimating the enemy is a great asset to those who are underestimated. The military and political capabilities of Yemen’s Houthi rebels have been underrated for nearly two decades. First, by the government of former Yemeni president Ali Abdullah Saleh, and then by Saudi Arabia and its supporters, including the United States.
From 2004-2010, the government of Ali Abdulla Saleh fought and lost six wars against the Houthis. The Houthi takeover of the Yemeni capital of Sana’a in September 2014 and their subsequent move southward toward Aden partly prompted Saudi Arabia and the UAE to launch their ill-fated intervention in Yemen in March 2015. The Saudis and Emiratis bet on a quick victory over the Houthis. Now, more than five years on, it is clear they have lost their bet. The Houthis and those allied with them have proved themselves to be resilient, capable, and strategically and tactically creative.
The Houthis and their allies have withstood five years of aerial bombardment, blockades, and attacks on multiple fronts by forces backed by Saudi Arabia and the UAE. Throughout the last five years, the Houthis have been outgunned, outspent, and subject to persistent aerial and satellite surveillance. Yet the intervention has not materially weakened them, and now, the Houthis are once again on the offensive across multiple fronts (al-Monitor, March 12).
The resiliency of the Houthis stems from their leadership’s understanding and consistent application of the algebra of insurgency. T.E. Lawrence used the term, or a version of it, in an article he wrote for Army Quarterly in 1920. The article, “Evolution of a Revolt,” argues that insurgents would be victorious if they applied certain “algebraical factors.”  These include force mobility and security as well as time and respect for the populace.  The Houthis broadly apply these and multiply them with superior human intelligence and an intimate knowledge of northwest Yemen’s daunting mountainous terrain. The Houthis, partly due to technical support from Iran, have also added drone and missile technology to the equation. These factors combine to make the Houthis a formidable force.
Move or Die
Force mobility has been—and remains—fundamental to the Houthis’ success in battling elements of the Saudi and Emirati militaries as well as those forces they support. These forces include Yemen’s internationally recognized government-in-exile, led by President Abdrabbuh Mansur Hadi, which is allied with Saudi Arabia, and a panoply of militias and armed groups supported by the UAE. The Houthis understand and readily apply what Chairman of the Joint Chiefs of Staff General Mark Milley explained in 2016, “on the future battlefield, if you stay in one place longer than two or three hours, you will be dead.”  General Milley made his comments in light of the widespread use of drones and other rapidly developing battlefield technologies.
The UAE’s and Saudi Arabia’s ability to field unmanned aerial vehicles (UAVs) has increased over the last three years. Both countries use Chinese manufactured UAVs in Yemen, most of which are operated by Chinese contractors as Riyadh and Abu Dhabi suffer from a lack of well-trained personnel. Saudi Arabia and the UAE also enjoy drone and satellite surveillance provided by the United States, which flies its own UAVs over Yemen on a daily basis.
In response to what, at times, has been persistent aerial surveillance, the Houthis make extensive use of highly mobile small combat units. These units are critical to the Houthis’ ability to defend territory, harass enemy forces, and plan and launch offensives. The combat units most often consist of no more than 20 men—roughly equivalent to a squad or specialized platoon—who rely on two or three light trucks and/or technicals. These trucks and/or technicals are easy to disguise and traverse Yemen’s worst roads and tracks.
Even smaller groups of men—equivalent to a fire team—are tasked with harassing enemy forces and collecting intelligence. The smaller teams may operate for weeks with all but minimal resupply. Most importantly, many of these units are not dependent on ranking commanders for daily or even weekly orders. The fire teams, or forward operating squads, are given a broad remit that remains in place until cancelled or amended. The Houthis are well aware that all electronic communications are monitored and consequently keep them to a minimum or use alternative means. These small, highly mobile units, especially the ones deployed along the edges of—and in—enemy-held territory operate on their individual commanders’ initiatives and seize on any vulnerabilities or opportunities they come across. 
Intense competition for spots in these combat teams takes place among those who aspire to rise up the ranks of the Houthi-led forces. Command within these units, from the lowest level to the equivalent of captains, is largely a meritocracy. Those who are most capable and successful are rewarded with rank, favors, and/or cash bonuses. On a deeper and more consequential level, the best fighters and commanders are the ones who survive by adapting to—and exploiting—the dynamic conditions in which they operate. Many, if not most, of the senior members of the Houthi leadership have firsthand experience in battle and are themselves the product of combat Darwinism. Only those who were capable and fortunate survived the years of fighting with the Saleh-led Yemeni government.
The Houthi leadership—at least parts of it—places a high value on bottom-up learning. While senior members of the Houthi family dominate the core leadership, the broader organization is open to those who possess the skills and talent that the group and their allies require.
The combination of what is largely a meritocracy with battlefield selection means that the Houthis and those allied with them benefit from motivated and creative officers and NCOs or their equivalents.  This contrasts with the forces arrayed against the Houthis and their allies. The armies of Saudi Arabia and, to a lesser degree, the UAE suffer from a pronounced lack of experienced and capable officers and NCOs. The UAE partly makes up for these deficiencies by employing mercenaries. The re-constituted “Yemeni Army” that is now fighting on behalf of Yemen’s government-in-exile also contends with poorly trained and ineffective officers and NCOs. Field grade and general officers in the re-constituted Yemeni Army most often achieve their ranks via personal connections to the Saudi Arabia-based government-in-exile. Furthermore, many of these senior officers are more interested in preserving their resources and thus sustaining their power and influence than engaging the enemy in protracted and costly battles.
Security and Intelligence
To a large degree, the mobility of Houthi forces ensures their security. The combat units that rove around their assigned sectors are indistinguishable from civilians since a significant percentage of Yemeni men in northwest Yemen carry weapons. Long before the start of the current war, bearing arms was a part of the culture. Additionally, the Toyota trucks used by the Houthis are as ubiquitous as the Kalashnikovs and G3 rifles carried by many across large swaths of Yemen.
The combat teams maintain their security by only massing when a target emerges that requires the combined firepower of multiple units. More often than not, a target such as a convoy (the Houthis’ largest source of weapons and material is coalition-backed forces) is first flagged by human intelligence. The Houthis maintain an informal but extensive human intelligence network that extends across Yemen and well into southern Saudi Arabia where they carry out hit and run raids on Saudi forces (al-Jazeera, September 29, 2019). Informants, who act out of loyalty and for material gain, pass along intelligence about enemy movements, proposed routes, and details about armaments and cargo to their handlers. The handlers then notify Houthi commanders charged with tasking. Combat units in the area through which the convoy or some other target will pass use a combination of human intelligence and hand launched drones to monitor the progress of a target. When the target approaches a predetermined area that is favorable to attack, combat units swarm the target by approaching from multiple directions. Once the attack is complete the units disperse.
Many of the combat teams that operate deep within enemy territory are semi-autonomous. The commanders of these units work their own human intelligence sources in their assigned areas, decide when to attack, and deploy hand launched drones to monitor and identify threats and opportunities. The autonomy helps ensure security by reducing electronic communication and nimbleness. Once an opportunity for engaging an enemy is identified, little or no chain of command exists to obtain permission to strike.
Human intelligence, like their small mobile combat units, is critical to the Houthis’ success on the battlefield. Via their extensive network of informants, the Houthis often know more about the location and capabilities of enemy forces than the general officers charged with commanding them.  Despite their enemies’ superior weapons, air support, and persistent overhead surveillance, the Houthis routinely anticipate and thwart offensives and counter-offensives. This is primarily due to the human intelligence that they receive from informants across Yemen. The Houthis’ use of numerous types of modified and indigenously produced UAVs allows them to confirm and augment the intelligence generated via informants. The pairing of human and UAV generated intelligence combined with the Houthis and their allies’ intimate knowledge of Yemen’s rugged mountains and canyons, acts as an effective force multiplier. The Houthis often anticipate the moves made by their foes and respond with deadly force. The accuracy of their responses means they are often able to “arrange the minds of their enemies” by eroding morale and undermining trust in the officers and commanders who lead the opposing forces. 
Anatomy of Failure
In contrast to the Houthis, the military forces opposing them suffer from slow and ineffective chains of command, dated and politically influenced intelligence, and poorly motivated men and officers. Decision making within the re-constituted Yemeni Army supporting the Hadi government is slow, top-heavy, and frequently compromised by in-fighting between rival politicians and military commanders. When orders are issued, they are often received by ranking commanders in frontline areas like Marib as suggestions rather than orders. This might be because the commanders have a better understanding of the situation or it may be the case that a particular officer and his backers think it advantageous to preserve their men and supplies.
The hoarding of supplies and the taking of a percentage of salaries by ranking officers was a problem in the Yemeni Army before the current conflict. These practices have continued and grown worse in the re-constituted Yemeni Army. The timely payment of salaries and distribution of supplies has a material impact on the willingness of many of the soldiers who have signed up to fight for the Hadi government. Most of these men, who are primarily from the south, only joined the Hadi-allied forces to collect a salary. Many of them have families who depend on the promised income. When these salaries are not paid or are reduced due to graft among ranking officers, many soldiers desert. In addition to low morale, a significant percentage of the soldiers listed on rosters are ‘ghost soldiers.’ They either do not exist, or, if they do, they are not actively involved in the fighting and are only on the roster to collect a percentage of a salary.
Saudi Arabia’s ‘blank check’ approach to the war in Yemen has exacerbated these problems. While indications that Saudi Arabia is cutting its expenditures in Yemen have emerged, the culture of corruption will persist. In fact, reduced aid from Saudi Arabia may mean that ranking officers and political figures are more inclined to preserve their resources to assure themselves a place in whatever political order follows.
As Saudi Arabia reduces its financial and military support for the Hadi government, the already limited effectiveness of its military will be further reduced. This is evident in the Yemeni governorate of Marib, where the Hadi government is struggling to hold the capital, Marib City. Despite air support from Saudi Arabia for Hadi’s military forces, the Houthis continue to gain ground. If Marib City falls to the Houthis and their allies, desertion rates among the opposing forces will soar and brittle chains of command will break.
The defeat of the Houthis has, according to many analysts and think tanks, been imminent for much of the past five years. The better equipped militaries of the UAE, Saudi Arabia, and their various proxy forces were supposed to rapidly defeat the Houthis and their allies. Great emphasis was placed on the technical superiority of the Western-equipped militaries of Saudi Arabia and the UAE. Yet despite the expenditure of vast sums on weapons and materiel by Riyadh and the Abu Dhabi, the Houthis have consolidated their control of northwest Yemen and are poised to capture the governorate of Marib.
The Houthis’ ability to defy and defeat technologically superior forces is a reminder that, as the military strategist and fighter pilot Colonel John Boyd argued, “machines don’t fight wars, terrain doesn’t fight wars. Humans fight wars. You must get into the minds of humans. That’s where the battles are won.”  The Houthis excel on the battlefield and this is unlikely to change, no matter how much Saudi Arabia, the UAE, and their backers spend on the war in Yemen. However, despite their military success, the Houthis may lose the core battle for the hearts and minds of Yemenis. Ironically, it is the end or reduction of hostilities that will most weaken the Houthis’ hold on power.
The war and their martial abilities are the Houthis’ greatest sources of legitimacy and support. Many of those who back the Houthis do so only for pragmatic reasons. For example, many Yemenis want to stop what they see as a foreign invasion by the UAE and Saudi Arabia. Yemenis of various political persuasions calculate that only the Houthis are capable of preventing outside powers from carving up Yemen. Others support the Houthis because they provide a measure of security and predictability, especially when compared with southern Yemen. Members of the Yemeni elite most often align themselves with the Houthis for financial and political gain rather than any shared ideology. The Houthis’ have, so far, stitched together impressive and durable networks of political and tribal support. However, alienation among a significant percentage of the population of northwest Yemen is growing due to Houthi abuses and their exclusivist policies. 
The Houthi leadership recently introduced a bylaw that stipulates that a percentage of the zakat—an obligatory tax and one of the five pillars of Islam—be paid to Hashemite families (al-Monitor, June 21). The Hashemites are those families who trace descent from the Prophet Muhammad’s great-grandfather. As Hashemites, this will benefit the Houthi family and the organization’s leadership. This bylaw, as well as what many view as the increasing influence of Iranian Jafari Shi’a religious practices, is drawing the ire of Yemenis—including Zaydis, a sect of Shi’a Islam followed by the Houthis.
While the Houthis will remain a martial and political force in northwest Yemen for the foreseeable future, resistance to the Houthi family itself will grow if the war winds down. Without the threat posed by the coalition and coalition-backed forces, the dominance of the Houthi family in the political arena of northwest Yemen will be more difficult to justify and sustain. Tensions within the core leadership will also threaten this dominance. The immediacy of war provides most of the cohesiveness that the Houthi leadership has enjoyed. Without the war, tensions within the core leadership will become more pronounced. As rival leaders attempt to broaden and reinforce power bases, there will be more space for old and emergent elites to reassert their authority. Over time this will lead to the dilution of the power held by the Houthis’ core leadership.
 See: Lao Tzu, Tao Te Ching (Shambala Edition, 2007).
 Thomas Edward Lawrence, “Evolution of a Revolt,” Army Quarterly 1:1 (1920).
 The Houthis are guilty, as all sides in the war are, of numerous and continuing human rights abuses. However, they do offer relatively high-levels of predictability and security for those living in the areas that they and their allies control.
 See: https://www.ausa.org/articles/radical-change-coming-gen-mark-milley
 Author interviews with Yemen based analysts and former government officials (June 2020).
 Many of the most capable officers and NCOs from the Yemeni Army and Air Force allied themselves with the Houthis following the Saudi led intervention. The Houthis continue to benefit from the expertise of these men, many of whom received training in the West as well as in former Soviet bloc countries.
 Author interview, Yemen based security analyst (June 2020).
 See: Liddell Hart, Colonel Lawrence: The Man Behind the Legend (Dodd, Mead and Company, 1934).
 See: Robert Coram, Boyd: The Fighter Pilot Who Changed the Art of War (Back Bay Books, 2002).