The controversial bombs are prohibited by multiple countries,

but they are part of an 800-million-dollar aid package the Biden administration says will strengthen Ukraine's offensive against Russian forces.

Russia has already spread tens of millions of these bomblets across Ukrainian territory.

Here's a breakdown of how the cluster munition works and why the United States plans on sending them despite humanitarian concerns.

US cluster munitions, also known as dual-purpose improved conventional munition,

are a type of weapon that spreads small bomblets over a wide area.

What DPICMs bring to a battlefield is anti-armor and anti-personnel capability.

A common type of cluster munition is fired in artillery shells, which is what the US is expected to give Ukraine.

They can also be in the form of rockets or dropped from a plane.

The weapon opens mid-air to release tens or hundreds of smaller explosive munitions or submunitions.

These submunitions can be loaded with charges that can penetrate armor

or munitions that can strike multiple human targets across an area as large as several football fields.

Clearly, a capability that would be useful in any type of offensive operations.

In Ukraine, Russia has used these munitions as far back as the first days of the invasion, according to Human Rights Watch.

The group said one attack struck residential areas in Kharkiv, killing at least three civilians.

Specifically, they say Russia has used 9M55K Smerch rockets.

Those are composed of submunition containers that have a tail fin and a fuse and sit at the front of the rocket.

The submunitions are designed to attack both people and equipment.

Behind those is the propellant.

After the rocket is launched, the container ejects the submunitions, commonly by combining an explosive charge and a spin mechanism.

When the fuse of each submunition is triggered⏤on the ground or in the air⏤it explodes.

But some of them can also fail to detonate.

These are referred to as duds, a common issue with cluster munitions.

Duds can cause long-term hazards as they may detonate after conflicts end and harm civilians.

Human rights groups say the first significant use of cluster weapons was by German and Soviet forces in World War II.

The munitions released by German planes were commonly called butterfly bombs,

with an attack on the British port of Grimsby, killing almost as many people after the raid as during it.

This bomb may go off as soon as it's even lightly touched.

It may also go off by itself up to half an hour after it's landed.

The US made extensive use of cluster munitions during the Vietnam War, also dropping them in neighboring Laos.

And since then, unexploded bombs dropped by American planes have killed or maimed thousands of Laotians.

More recently, during the war in Iraq, the US showered more than 1 million bomblets during a 3-week period of major combat.

Since 2008, more than 110 countries have signed an international convention on cluster munitions

that prohibits all use, transfer, production, and stockpiling of cluster bombs.

Russia and Ukraine have not signed the agreement, and the US is among several other NATO countries that are also not signatories.

The DPICM ammunition we are delivering to Ukraine will consist only of those with a dud rate less than 2.35%.

Compare that to Russia, which has been using cluster munitions across Ukraine, with dud rates of between 30 and 40%.

Cluster munitions are already being used by both sides in the war in Ukraine.

The difference is that Russia is using cluster munition to attack, to invade Ukraine.

Ukraine is using cluster munition to protect itself against an aggressor.

According to Human Rights Watch, Ukraine inherited a stockpile of cluster munitions after the breakup of the Soviet Union,

and the Biden administration decided to provide US cluster munitions after written assurances that the weapons wouldn't be used in civilian areas.

Even allies who were signatories to the Oslo Convention,

while they cannot formally support something that they've signed up to a convention against,

have indicated, both privately and many of them publicly, over the course of today that they understand our decision.

The Pentagon says the cluster munitions could be effective when used against Russian armored formations and trench lines,

and US officials have defended the decision to supply the weapons as necessary

to prevent Ukraine from running low on artillery ammunition at a critical stage in the conflict.

By providing Ukraine with DPICM artillery ammunition,

we will ensure that the Ukrainian military has sufficient artillery ammunition for many months to come.