Fractionalization of Spanish military
The breakup of Spanish armed forces of July 1936 was the process of decomposition of the Second Spanish Republic's military and public order formations into two factions: the one which supported the government (loyalists, later called Republicans) and the one which joined the coup (rebels, later called Nationalists). Theoretically there were some 250,000 men serving in various armed branches. However, in fact this figure was probably much closer to 170,000, of which 90,000 served in the military and 80,000 in public order formations; detailed figures advanced by historians differ.
In historiography the prevailing opinion is that more armed servicemen joined the rebels than the loyalists; the ratio advanced differs from 62:38 to 52:48, yet there are also scholars who claim that only the minority joined the insurgency. It is usually accepted that slightly more peninsular troops and slightly more public order men remained loyal rather than rebelled, but that the so-called Army of Africa, which in its entirety joined the coup, tilted the balance in favor of the Nationalists.
Numerical split of manpower between the two warring sides of the Spanish Civil War is by no means indicative as to division of military and combat potential. This is mostly because in the Republican zone the effectives theoretically available were not taken advantage of; many military units were dissolved as potentially rebellious, many officers were detained, many units with few officers and NCOs left turned into loose undisciplined groupings, many rank-and-file servicemen opted for a wait-and-see stance and many later crossed to the Nationalist zone. Also, in early days following the failed coup the military potential of both sides was to a significant extent defined by civilian volunteers.
Military.
The Spanish military forces were falling into 3 major groups: 1) mainland army, stationed in garrisons in peninsular Spain and on the islands; in numerical terms it was composed mostly of conscripts. Most scholars do not hold these troops in high regard, suggesting poor quality of training, low morale, outdated equipment and officers who often have never seen combat, resembling bureaucrats in uniforms rather than military commanders. These troops were organised into 8 so-called organic divisions, each corresponding to one military region; their theoretical strength is usually quoted as 110,000-120,000, but in July 1936 there were no more than 70,000 actually in the barracks; 2) army stationed in Africa. It consisted of heterogeneous formations, but mostly of indigenous Moroccan troops and the Foreign Legion, both composed of volunteers. Most of its officers and NCOs saw combat during Rif Wars. African troops were widely considered the best part of the Spanish army; they numbered some 24,500 men in actual service; 3) the navy. In terms of manpower there were some 12,000 people serving in its ranks; the fleet was composed of rather obsolete larger warships and numerous newer destroyers, with some modern cruisers near completion in shipyards. Peninsular and African troops were governed by the Ministry of War; the fleet was governed by the Ministry of Marine. Air force, which technically formed a separate branch, in terms of manpower grouped no more than few thousand men.
Peninsular army.
 Conscripts, Gipuzkoa
 claims that in the mid-1930s, there were 140,000 military on the continent and islands in total; Quesada gives the theoretical figure of 120,000; Beevor opts for some 110,000. Clifford adheres to the theoretical figure of 120,000, but notes that only 80,000 were actually available. These figures stand no comparison to calculations of military historians, who claim that "de facto" there were some 65,000 troops in all peninsular garrisons; retrospective analysis of the Francoist staff claimed 60,000. Fairly recent analysis of the Republican army during the civil war, written by , claims that the total number of troops actually in the barracks in July 1936 was some 65,000. The record high figure of 78,000 is suggested by Hooton, while the record low figure is advanced by , who gives the total of 45,000. How this mass was split between the Republicans and the Nationalists is unclear, e.g. at times totals advanced by various authors do not match their own sub-totals. claimed 32,000 Republicans and 19,000 Nationalists (63:37), Nationalist staff had 36,500 Republicans and 23,500 Nationalists (61:39), Quesada claims 33,000 Republicans and 24,000 Nationalists (58:42) and exactly the same figures are given by Turnbull, Beevor settles for 57,000 Republicans and 50,000 Nationalists (53:47), opts for 35,000 Republicans and 32,000 Nationalists (52:48) and almost exactly the same figures are advanced by Alpert, 34,000 Republicans and 32,000 Nationalists (52:48), repeated also by Thomas and Platón. The same proportion of 52:48, but much lower totals are advanced (with detailed figures broken down into divisions and branches) by Arzanegui: 27,000 Republicans vs 25,000 Nationalists. Hooton comes out with 40,000 Republicans and 38,000 Nationalists (51:49), while Payne maintains that “less than half” of “fewer than 90,000” rebelled (47,000 Republicans, 38,000 Nationalists?). Some scholars, who accept the figure of 66,000 troops actually in the barracks on the peninsula, settle for general remark that they were “spread roughly equally”. Puell is the only scholar who claims that most peninsular troops joined the rebels: 21,600 Republicans vs 23,600 Nationalists (48:52). In structural terms, out of 8 divisional commands 3 were controlled by the Republicans (, , ) and 5 by the Nationalists (, , , , ).
African army.
Some earlier works, e.g. , claimed that the Army of Africa consisted of some 47,000 troops; also some recent books advance similar figures, e.g. Beevor and refer to 40,000; Hooton claims 36,000 while Puell and Thomas give the number as 30,000. However, there was no homogeneous formation known as “Army of Africa” and Spanish Morocco was garrisoned by at least 4 different formations: 1) Foreign Legion, 2) indigenous troops in Spanish service, so-called "Regulares", both infantry and cavalry, 3) indigenous troops in service of the sultan and 4) Carabineros, plus 5) minor figures related to navy, air force and policing formations. Already some older studies claimed that there were merely 24.5 thousand troops available to the Nationalists in Morocco, and the figure of 24,741 is advanced also by the recent military analysis. The difference, apart from usual issues related to leaves and outdated documentation, is due to some categories, especially troops in sultan's service, formally not having been under Spanish command and not having been available for shift towards the peninsula. All sources agree, however, that troops brought to Spain from Morocco were the best units in the army, battle-hardened during the Rif Wars, well-equipped and with high combative spirit. Almost all of these 25 thousand men joined the Nationalists, with the exception of some 300 men on leave on the peninsula.
Navy.
Though in terms of land forces the potential of Spanish army was rather limited and in numerical terms it was smaller e.g. than the armies of Poland, Romania or Czechoslovakia, its navy still ranked as a powerful force to be reckoned with. In Europe it ranked far behind the British and French fleets, but until the early 1930s it was still comparable to the Soviet navy (Europe), German Reichsmarine/Kriegsmarine and the Italian Regia Marina, outclassed only when the latter three embarked on massive investment program. Salas estimated total naval personnel at 20,000, yet contemporary military historians reduce this figure to some 12,000 men. Quesada claims that 7,000 joined the rebels (with no info either on total or how many remained loyal), and Thomas gives the explicit split of 7,000 rebels vs 13,000 loyalists. This, however, is of limited importance; what mattered was the split of warships available. In terms of tonnage, the Republican fleet was double the size of the Nationalist one (some 60,000 tons vs. some 30,000 tons), which was mostly thanks to Nationalist control over 1 battleship (16,000 tons). In terms of the number of warships the Republican advantage was massive: they operated 1 battleship, 3 light cruisers, 14 destroyers and 12 submarines, while the Nationalists operated 1 battleship, 1 light cruiser, 1 destroyer and no submarine. The Republicans controlled all ports along the Bay of Biscay and on the Mediterranean (some 80% of all coastline), while the Nationalists controlled ports in Galicia and on the Atlantic coast of Andalusia.
Total military.
Officers on manoeuvres (1936)
Almost no author provides overall military figures (peninsula + Africa + navy) and in most cases, their suggestions must be ascertained by means of adding sub-totals or applying partial ratio calculations. For Puell it is 21,600 Republicans vs 53,600 Nationalists (29:71), for Romero Salvado it is 35,000 Republicans vs. 66,000 Nationalists (35:65), for Beevor it is 57,000 Republicans vs. 100,000 Nationalists (36:64), for Hooton it is 39,800 Republicans vs 74,000 Nationalists (36:64), for Quesada it is 33,000 Republicans vs. 53,000 Nationalists (38:62), for Turnbull it is 33,000 Republicans vs. 48,000 Nationalists (41:59) and for Thomas 50,000 Republicans vs 71,000 Nationalists (also 41:59). The narrative by Payne implicitly suggests the same ratio, but somewhat higher figures, namely 47,000 Republicans vs. 68,000 Nationalists (41:59).
The officer corps got split fairly evenly; recent military estimates suggest that out of 17,000 officers in total (inc. retired etc.), 8,000 found themselves in the Republican zone and 9,000 in the Nationalist one (47:53). However, in fact only 4,000 supported the loyalists and 13,000 opted for the rebels. Another author claims that out of officers active and in service, 2,000 opted for the Republicans and more than 4,600 for the Nationalists. One more scholar claims that for all officers in active command, 3,000 supported the Republicans and 5,900 sided with the Nationalists. For NCOs the numbers were 7,500 in the Republican zone and 8,000 in the Nationalist one.
Public order forces.
 Miqueletes on parade, 1934
Apart from regular military, there were 3 other major uniformed and armed formations. None of them was formatted as combat troops, intended to take part in tactical warfare operations. However, they consisted of disciplined men in structured, barracks-based units, trained to perform policing role and to use firearms. The traditional constabulary, operational mostly in rural areas, was Guardia Civil (some 34,000 men). Another traditional service was Carabineros (formally Instituto de Carabineros), operating mostly along the frontiers to prevent smuggling (sources provide figures ranging from 14,000 to 16,000). Relatively new service was Guardia de Asalto (formally Cuerpo de Seguridad y Asalto), set up by the Republic (some 18,000). The "Civiles" and the "Asaltos" were subordinated to the Ministry of Interior; the Carabineros formed part of the Ministry of Finance structures. There was no service named “police”. However, there were some specialized armed services, e.g. traffic rules were enforced by Cuerpo de Vigilantes de Caminos. There were also various armed policing services subordinated to local authorities, be it regional or province-specific. Strength of these other units is highly unclear, though they might have amounted to 14,000. Total number of servicemen in all security formations was about 80,000.
Guardia Civil.
By far the largest security formation in Spain was Guardia Civil; in sources its strength is quoted as 32,458, 32,477, 32,860, or 34,320. Its units were scattered evenly across all of the country, though with higher saturation in rural areas and small towns rather than in large urban centres. Its commander, general Sebastián Pozas Perea, was a loyal though not particularly vocal republican. The "Civiles" had a long-standing reputation of heavy-handed service, and were despised by left-wing supporters as an instrument of reactionary politics. Some sources claim that most of the servicemen joined the rebels; Beevor maintains that merely 40% (which would translate to 13,000-14,000 men) remained loyal. However, academic scholars tend to disagree; according to some 51% sided with the government, the popular Osprey series by Quesada suggested rather 53%, Thomas claims 56% while earlier Osprey work by Turnbull suggested 59%; this is the ratio advanced also by Osprey booklet by Lannon, by the Nationalist staff quoted by Payne (20,100) and by Platón (20,120). Depending upon the ratio estimated and overall strength assumed, in absolute terms these percentages would translate to some 16,000-20,000 "Civiles" in the Republican ranks and 13,000-16,000 in the Nationalist ones. There is abundant evidence of Guardia Civil taking part in combat during the July coup, either on the rebel or on the loyalist side. There seems to be no particular pattern emerging, and even in one area local garrisons might have adopted a different stand, e.g. in the Seville province some rebelled (in Ecija), some suppressed the rebellion (in Carmona) and some assumed a wait-and-see position (in Osuna).
Guardia de Asalto.
Sources tend to agree that the