For a second everyone froze. An eery whooshing sound high above announced an incoming shell from South African artillery. The earth trembled as clouds of dust and smoke rose from the site of impact less than a thousand yards away. The shelling has become routine here, as a South African-led force of 8,000 troops drives to capture the shattered town of Cuito Cuanavale. Defending the area are about 10,000 Angolan troops, backed by thousands of Cuban soldiers and advisers.
The battle for Cuito Cuanavale has become one of the biggest, in numbers of troops and fire power, military clashes ever in Africa. Most analysts see it as a pivotal test of wills in the Soviet-backed government's 13-year-old war against South Africa and the rebel movement it sponsors, the National Union for the Total Independence of Angola (UNITA).
Shelling by South African mobile artillery guns can last up to three hours. But Angola's Army, inhabiting an underground world of bunkers and trenches, appears impervious.
``We are not going to permit the South Africans to take Cuito. ... the South Africans are going to have to pass through us,'' vowed Major Armindo Morreira, the Army's political commissar in the embattled province of Cuando Cubango.
The South African Defence Force (SADF) and UNITA began their siege of Cuito Cuanavale late last year, after South African artillery staved off an Angolan assault on the town of Mavinga. Had the Angolans captured Mavinga, it would have had a clear shot at UNITA's headquarters at Jamba further south.
But the onslaught appears to have stalled after fighter jets, piloted by Cubans and Angolans, halted a SADF thrust in mid-January, creating a stalemate.
Angola's dug-in force, including crack Cuban ``ranger'' special forces, is holding on. Angolan commanders warn of an imminent South African assault, but feel confident that the tide of the war is turning against Pretoria. Cuito Cuanavale, said some, is Angola's Stalingrad.
Indeed, time is becoming South Africa's enemy in southern Angola.
Thirteen years of fighting the SADF, intensive training by Cuban and Soviet advisers, and massive supplies of Soviet military hardware have forged Angola's armed forces into a battle-tested army.
With more accuracy, the Army's anti-aircraft gunners are downing South African ``mirage'' attack planes. South Africa's casualties, including whites, are up.
There is no sign that South Africa has carried out a pre-Christmas vow to begin withdrawal from Angola. And Pretoria's aging Air Force fleet is being depleted.
``The South Africans are embarrassed. They used to think that invading Angola was a tourist trip,'' said Capt. Brancao Armindo Fraternidade, a commander in Cunene Province. ``But gradually we are making things more difficult for them.''
The Angolans' confidence is bolstered by the belief that while an international arms embargo and stepped up security against domestic unrest are beginning to stretch Pretoria's Army, increasing oil production and revenues, and new Western-style economic reforms should buoy their war-weary economy.
Still the SADF remains the most powerful military force in Africa. Raids on Feb. 20 and Feb. 25 on the outskirts of the strategic southwestern town of Lubango demonstrated that South Africa's ace pilots are still capable of exploiting gaping holes in Angola's air defense.
The risk Angola's Army runs by concentrating its forces in Cuito Cuanavale is of leaving wide tracts of land behind the lines open to UNITA guerrilla raids. In recent weeks, Angolan officials admitted, UNITA has captured several small towns north of here.
South Africa also faces a dilemma in Cuito Cuanavale. Even if the SADF manages to capture the town, the Army and its Cuban allies, now nearly 40,000 strong, could withdraw and begin a counterattack. Should the South Africans opt for a pullout, their retreating forces would be an easy target for strafing runs launched from the Angolan airbase at Menongue.
Yet South Africa's assault on Cuito Cuanavale strengthens its position both as protector of UNITA and as a regional power to be taken into account in any peace talks brokered by US Assistant Secretary of State Chester Crocker.
Mr. Crocker's attempts at a settlement brought him to the negotiating table in Luanda, Angola's capital, on Jan. 28 with Cuba's foreign affairs chief, Jorge Risquet, and Angolan President Eduardo dos Santos.
Both sides agreed that the talks made progress on a plan to trade the withdrawal of Cuban troops from Angola for a pullout of South African forces, an end to the aid Pretoria and Washington provide to UNITA, and independence for neighboring Namibia (South-West Africa), which Pretoria rules in defiance of UN resolutions to withdraw.
But many observers believe South Africa wants nothing to do with the agreement, preferring to keep the Cubans in Angola to justify the SADF's occupation of Namibia.
This weekend, South Africa Defense Minister Magnus Malan put forth a new proposal to set up a neutral government in Angola. The proposal excluded the US and barely mentioned South African rule in neighboring Namibia, which US and South African negotiators have previously linked to any Angolan solution.
``South Africa's message in Cuito Cuanavale is clear,'' said one Western diplomat. ``Everybody can forget about any kind of deal in Angola until Pretoria says so.''