Washington: The Pentagon revealed on Tuesday that it overestimated the cost of the weapons it sent to Ukraine over the previous two years by $6.2 billion, or roughly double early estimates, leaving a surplus that will be put towards future security measures. According to Pentagon spokeswoman Sabrina Singh, a thorough investigation into the accounting error revealed that the military services had sent equipment to Ukraine at replacement costs rather than at book value. According to her, after all the numbers were added up, there was a $3.6 billion error in the current fiscal year and a $2.6 billion error in the 2022 fiscal year, which ended on September 30. The result is that the department has more funds available to support Ukraine as it continues its counteroffensive against Russia. Additionally, it happened as the fiscal year was coming to an end and congressional funding was starting to decline. Also Read: Ukraine's allies promise to hold Russia accountable for its invasion According to Singh, "it's just going to go back into the pot of money that we have allocated" for the upcoming Pentagon stock drawdowns. The information is released as Ukraine advances with the initial phases of its counteroffensive in an effort to drive out Russian forces from territory they have occupied since a full-scale invasion in February 2022. Valerii Zaluzhnyi, the head of Ukraine's armed forces, said that the counteroffensive has run into heavily mined terrain and strengthened defensive fortifications. In the meantime, Russia has been launching dozens of Shahed drones that explode over the Kyiv region in an attack that has revealed gaps in the nation's air defence after nearly 16 months of war. Russian drones were launched early on Tuesday, according to officials, but 32 of the 35 were shot down by Ukrainian air defences. The Pentagon has frequently used the presidential drawdown authority to remove arms, ammo, and other equipment from the shelves in order to reach Ukraine much faster than by going through the traditional purchasing process. According to previous projections made public on June 13, the US had given Ukraine security assistance worth more than $40 billion since Russia's invasion. The US has actually given less than $34 billion in aid, according to the new estimate. The precise sum of funds still available for the drawdowns or the Ukraine Security Assistance Initiative, which provides longer-term funding for the acquisition of weapons, including some of the more substantial air defence systems, has not been disclosed by officials. Also Read: UN rapporteur urges Indonesia to take the initiative in resolving the crisis in Myanmar In response to Russia's invasion, the US has approved four rounds of aid to Ukraine totaling about $113 billion, some of which will be used to resupply US military equipment that has been deployed to the front lines. The most recent round of aid for Ukraine and NATO allies, totaling about $45 billion, was approved by Congress in December. The package was intended to last until the end of the fiscal year in September, but a lot depends on what happens in the real world, especially as the new counteroffensive intensifies. The US will support Ukraine "as long as it takes" to repel the Russian forces, according to President Joe Biden and his senior national security officials. Secretly, administration representatives have warned Ukrainian leaders that the American public and Congress have a finite amount of patience with the costs of a conflict with no clear end in sight. Also Read: H-1B Visa Reboot: US Unveils Game-Changing Plan During PM Visit Congressmen have repeatedly questioned Defence Department officials about the degree to which the US closely monitors its aid to Ukraine to make sure that it is not subject to fraud or falling into the wrong hands. Depending on the sensitivity of each weapon system, the Pentagon claims to have a "robust programme" to track the aid as it enters Ukraine and to monitor it once it is there. According to Singh, the accounting error won't stop aid from continuing to be delivered to Ukraine.