US-made MK-84 bombs are capable of ripping through thick concrete and metal, and can instantly kill anyone within their wide blast radius.
The Biden administration stopped sending the 2,000-pound (907 kilogram) bombs to Israel after conceding they were killing civilians in Gaza.
But, soon after being sworn in, US President Donald Trump lifted the export block.
Now the flow of the weapons has restarted.
Israeli Defence Minister Israel Katz welcomed the delivery over the weekend, calling it "a significant asset for the Air Force and the IDF (Israel Defence Forces)" and thanked the US for its "unwavering support".
The bombs arrived in Israel as negotiations were set to ramp up on phase two of the Gaza ceasefire deal.
Experts say it is intended to send a message across the region.
Biden's stance reversed
The US had been providing Israel with the bombs, often referred to as "bunker busters", since the Israel-Hamas conflict broke out in October 2023.
But as Israel planned to invade Rafah in southern Gaza last May, president Joe Biden drew the line.
With more than a million Palestinian civilians sheltering in the area, he halted the shipment of about 1,800 MK-84s.
"Civilians have been killed in Gaza as a consequence of those bombs and other ways in which they go after population centres," Mr Biden said.
"I made it clear that if they go into Rafah … we're not going to supply the weapons."
The bombs are designed to penetrate hardened, deeply buried underground targets.
The explosions are so immense that weapons experts say they can "pancake" entire buildings.
Marc Garlasco, a former Pentagon defence official and a UN war crimes investigator, has cautioned that an explosion in the open would mean "instant death" for anyone within about 30 metres.
Sending a message to Hamas
Mr Trump said he lifted the export block on the weapons despite a ceasefire agreement being in place because he believed in "peace through strength".
"Biden wouldn't deliver the weapons. But I look at it differently. I say, 'peace through strength,'" Mr Trump told reporters
"They were sitting there. Nobody knew what to do with them. They (Israel) bought them."
The shipment arrived after days of concern about whether a fragile ceasefire in Gaza agreed last month would hold, after both sides accused each other of violating the terms.
Malcolm Davies, senior analyst in defence capability at the Australian Strategic Policy Institute (ASPI), said the timing of the weapons delivery was a strategic move.
"It sends a message to Hamas and Iran that if Hamas does not continue to observe the ceasefire arrangements, then Israel will return to war, and they'll have much more devastating weapons," he told the ABC.
Israel was also positioning itself to go after Iran's underground nuclear facilities, he added.
"There is increasing concern that Iran, in coming weeks or months, could decide to try and get nuclear weapons," he said.
"By giving Israel these heavy bombs, Israel is better equipped to go after Iranian nuclear facilities and destroy that threat before it becomes real."
'Nothing is off the table'
The ceasefire's first phase ends in two weeks.
Negotiations were meant to begin two weeks ago on the second phase, in which Hamas would release dozens of remaining hostages in exchange for more Palestinian prisoners and detainees, a lasting truce and the withdrawal of Israeli forces.
Sascha Dov Bachmann, a professor of law and security at the University of Canberra, said the delivery of the heavy bombs was another indication of Mr Trump's "unrestricted and complete support" for Israel.
"He is signalling to Netanyahu and his supporters that America has your back, and you can do what you want," he said.
"Basically, nothing is off the table."
Bomb use raises legal questions
The Biden administration had also displayed "unwavering" support for Israel, including participating in its defence during two missile attacks by Iran.
But Professor Bachmann said Mr Biden's policies were still often driven and informed by international and domestic legal considerations.
There has been heated debate around the use of heavy weapons such as the MK-84 bombs in Gaza over the risk of large numbers of civilian deaths.
The bombs are not banned, but the legality comes down to how they are used.
The statute of the International Criminal Court lists as a war crime intentionally launching an attack when it is known that civilian death or damage will be "clearly excessive" compared to any direct military advantage.
The MK-84 can be fitted with guidance systems, but most remain unguided, Professor Bachmann said.
"From an international humanitarian legal point of view, it becomes a little bit complex when it comes to fighting in an urban environment," Professor Bachmann said.
"The problem in Gaza is that the whole battlefield is a civilian urban area."
The Arms Trade Treaty also forbids weapons transfers "when there is a defined level of risk that war crimes or serious violations of international human rights law will be committed".
The UN and human rights organisations, including Action on Armed Violence (AOAV), have warned of their use in Gaza.
"The history of air-dropped bombs like the MK-84 tells us that their use in densely populated regions will almost certainly lead to indiscriminate civilian harm," Iain Overton, executive director of AOAV, said.
"There needs to be a far greater emphasis on minimising the humanitarian cost of these weapons."
Professor Bachmann said that Mr Biden reviewed whether Israel's use of the bombs could be in breach of humanitarian laws and made the call to halt the transfers.
"Trump basically says it doesn't matter, and that is dangerous," he said.
ABC/Wires
