The defenders were somewhat aided by fortifications from previous eras, including a major Imperial Russian-era fortress complex at Osowiec on the Biebrza River that was a scene of several battles during the First World War.

The approaches to Osowiec were heavily defended; the 1st Guards Assault Engineer Brigade was required to establish river crossings under fire.

[3] Units of the Front stormed and took the fortress, after a heavy air bombardment by Major-General Georgy Baydukov's 4th Assault Aviation Corps, on 14 August.

The 49th Army, however, found that the German defences on the approaches to Lomza were difficult to overcome, sustaining many casualties (even losing a divisional commander, Major-General Yakimovich of the 343rd Rifle Division, in their attempt to force the defensive lines).

Although there were many local actions (including attacks by Polish partisans, who had a strong presence in the area) the German defence line on the Narew held through the remainder of 1944, until the 2nd Belorussian Front's advance in the East Prussian Operation of January 1945.