The struggle for control of Radzymin forced General Józef Haller, commander of the Polish Northern Front, to start the 5th Army's counterattack earlier than planned.

While the unit's core was formed around veterans of the 2nd Polish Rifle Division of the French-equipped and trained Blue Army, it had been recently reinforced with fresh, but raw, recruits.

[10] The Polish line ran some 2 kilometres (1.2 mi) in front of the town, from the unfinished 1909 Fort Beniaminów at the banks of the river Bugonarew through Mokre to Dybów.

The terrain was mostly flat; numerous roads converged radially along an arc from the Modlin Fortress to the north (where the Narew flows into the Vistula), to Legionowo, Radzymin, and Mińsk Mazowiecki directly to the east.

However, its 21st Rifle Division remained on the south side of the Bug River and headed for Warsaw directly, under orders from Russia's Commissar of War Leon Trotsky.

[23] Deprived of artillery support, the inexperienced and overstretched[31][34] 1/46th Infantry Regiment, defending the village of Kraszew, broke, and the Soviets gained entry to Radzymin.

[37] One of the artillery officers noted that the Russians achieved complete tactical surprise: "I ordered my dinner prepared when my aide came shouting 'Lieutenant Sir, the Reds are in the city'".

While ultimately unsuccessful, the battalion forced the Russian troops to remain stationary overnight, giving the Poles badly needed time to regroup and receive reinforcements, which came in the form of a single regiment from the 1st Lithuanian-Belarusian Division.

[28][34][40] The following day the battlefield was visited by, among others, Prime Minister Wincenty Witos, papal nuncio Achille Ratti (the future Pope Pius XI),[41] Maciej Rataj and General Józef Haller, the commanding officer of the Northern Front.

General Haller's dispatch of 01:00 hours the same night called the Polish defeat at Radzymin "ignominious", and ordered the commanding officers of the 46th Infantry Regiment and divisional artillery to be immediately court-martialled.

[36][b] The gravity of the situation was well understood by the Polish Commander-in-Chief Józef Piłsudski, who remarked that all the battle plans for his counteroffensive were based on the assumption that Warsaw would hold,[34] and suggested to General Tadeusz Rozwadowski that he reinforce the Radzymin area with any forces available, including an "en masse tank attack".

[42][c] The loss of Radzymin also forced General Władysław Sikorski's 5th Army, fighting north of the Bug River and along the Vistula, to start a counteroffensive from the Modlin Fortress earlier than planned.

[34] Rozwadowski and General Maxime Weygand, a member of the French Military Mission to Poland, even suggested that Piłsudski also hasten his preparations for a counteroffensive, but he refused and decided to follow the original plans.

[38] At 10:15 hours the Polish 81st and 85th Infantry Regiments from the 1st Lithuanian-Belarusian Division assaulted the left flank of the unsuspecting Russians,[46] continued along the Warsaw–Białystok road, and broke through to the town.

[46] The success did not last long, as the Russian 27th Rifle Division turned around and arrived at Radzymin just in time for its 81st Brigade to push the exhausted Polish forces back towards the village of Słupno.

[38][47] Threatened by further attacks from Słupno and Wieliszew, the 85th Regiment retreated after suffering heavy casualties, including the commanding officer of the 1st Battalion, Captain Ryszard Downar-Zapolski.

[46][48] The Soviet advance was halted, and this time chaos in the Polish ranks was avoided, but again lack of reinforcements behind the main line of defences proved a serious problem.

[38] In the evening Generals Lucjan Żeligowski, Józef Haller, Jan Rządkowski and Franciszek Latinik met in Jabłonna and again in Struga to prepare a plan for retaking Radzymin once again.

A single battalion from the 28th Kaniów Rifles Regiment from the 10th Division, led by 1st Lieutenant Stefan Pogonowski, was ordered to entrench in a forest near Wólka Radzymińska and organise an ambush.

The rest of the Polish forces were to start an all-out assault at 05:00 hours the following morning, with General Żeligowski in command over the ad hoc corps.

[33] This, however, did not pose an immediate threat to the defenders of Warsaw, as its advance was finally halted at the outskirts of Włocławek, and it was forced to start a hasty retreat eastwards.

Both Polish assaults were bloodily repelled, with the casualties including Lieutenant Pogonowski who was posthumously awarded the Virtuti Militari medal for his bravery leading the charge, but they did force the Russians to retreat to their initial positions.

Although the Russian side had superior artillery and brought several Austin-Putilov armoured cars, this time the Polish assault was supported by five Renault FT tanks and numerous aircraft.

[50] Despite suffering from mechanical failures, the tanks successfully broke through the Russian lines, and the infantry of the 85th "Wilno Rifles" Regiment from the 1st Lithuanian-Belarusian Division followed them into the town.

Instead of waiting for orders from General Żeligowski, the commanding officer of the 10th Division, Lieutenant Colonel Wiktor Thommée, started a push along the southern bank of the Bugonarew.

[46] The 28th and 29th Kaniów Rifles Infantry Regiments managed to reach the village of Mokre, on a small hill overlooking Radzymin and the Białystok-Warsaw road, directly behind the Russian lines.

In the early hours of August 16, the Russians mounted yet another assault on Radzymin, reinforced by several armoured cars and led personally by the commanding officer of the 27th Rifle Division, Vitovt Putna.

[52] After the barrage ended Lieutenant Colonel Wiktor Thommée personally led his forces in a bayonet charge; the regiment re-entered Mokre at noon and the Russians fled.

[50] This made existing Russian plans obsolete, and Polish forces started a pursuit that ended with the victorious Battle of the Niemen River in September.

[3] It was noted by General Lucjan Żeligowski that the importance of the northern approach to Warsaw was poorly understood by the Polish commanders prior to the battle and that the untested and relatively weak 10th Division was chosen for the task of defending Radzymin "out of sheer incompetence".