Israel's move to ground operations in the Gaza Strip gives Palestinian militants their first chance to trade blows on a more or less equal footing with the Israeli army in the current conflict.
Hamas is by nature a secretive organisation. However, analysts believe it has considerably enhanced its military capability since taking control of the Gaza Strip in the summer of 2007.
Hamas has had to smuggle all its other weaponry into Gaza - which is under a complete blockade imposed by Israel and supported by Egypt in the south.
This is done via tunnels under the Egypt-Gaza border, which have furnished Hamas with the medium-range rockets that have hit Israeli cities up to 25 miles (40km) away.
Explosives and the ingredients for explosive and rocket propellants are even more easily smuggled into Gaza.
Mortars, anti-tank weapons and some anti-aircraft weapons - not effective against modern jet fighters, but possibly so against older helicopters - are also thought to have come through the Rafah tunnels.
So it was an unsurprisingly bellicose Khaled Meshal, Hamas's Damascus-based leader-in-exile, who spoke in an Arabic TV interview before ground operations began on Saturday night.
"Soldiers of the enemy... you must know that a black destiny is waiting for you, and you will either be killed, injured or imprisoned," he told al-Jazeera television.
The Hamas military wing - the Izz al-Din Qassam Brigades - is thought to have about 15,000 members.
It is therefore vastly outnumbered by Israel's total military capability. But there is no shortage of weapons in Gaza or people who might want to pick up a gun against Israelis forces.
Standards of training and discipline for the Brigades have been raised recently, and it is believed to have fairly sophisticated communications systems.
The organisation has clearly learnt lessons from the 2006 Lebanon war, when Hezbollah bloodied Israel's nose in a bruising encounter in terrain ideal for guerrilla warfare against a conventional army.
Since then, a number of Hamas members are thought to have spent time with Hezbollah and Iran's Revolutionary Guards movement - leading to improvements in its military training regime and organisational system.
The geography of Gaza may not be as advantageous as south Lebanon, but doubtless many Izz al-Din Qassam Brigades members will be hoping to deal a blow against the Israeli army and be rewarded with what they consider glorious martyrdom in the process.
Source:BBC News