Barring a decision on how to pay for it, it’s likely we’ll see a Royal Commission into the allegations of sexual crime in the DLA Piper report.

The questions of whether the ADF still has a culture that condones sexual violence and bullying, whether alleged sexual criminals are still serving in the ADF, and whether the ADF did a good enough job of investigating reports can only be answered by an investigation external to defence. But a Royal Commission will be enormously damaging to the ADF at a critical moment in its history, regardless of the factual outcomes.

The damage caused by those alleged to have preyed on their weaker military peers is not yet complete.

Defence will be unable to conduct the investigation into these alleged offences internally for several reasons. First, the sheer scale of the allegations would swamp any organisation’s investigative capabilities. And defence does not have a great record of efficiently investigating itself.

Efforts to investigate and prosecute alleged offences committed by commandos in Afghanistan were highly contentious, slowly processed, led to emotionally charged debate within the organisation, and ended prematurely having established few facts. The Commonwealth Defence Force Ombudsman concluded in a 2009 report that there were numerous deficiencies in the way defence conducted investigations and that multiple reviews (including one external review in 2004) “did not seem to have produced decisive, measurable reforms or improvements”.

This week, internal documents released under freedom of information provisions outlined concern amongst senior defence leaders that the military’s police service “lack the requisite investigative capability to properly manage and investigate service offences committed by ADF members”. That service is already committed to a range of investigations within Australia and overseas and has nowhere near the capacity needed to investigate an additional 700 alleged s-xual crimes.

Institutions such as defence and churches often struggle with the aggressive investigative action needed to get to the bottom of seemingly pervasive scandals such as this. Internal investigators must go back to working inside the organisation when the investigation is done, their values are the same as the people they are investigating. Sometimes that is an asset, other times it is an obstacle.

A sweeping organisation of this scale requires external investigators with no entrenched interests, few confirmed biases, and the tenacity to cut through assumptions about the proper investigatory cadence. And only external investigators can assuage the public perception that defence cannot be trusted to investigate itself.

The investigation will need the power to compel witnesses to appear before it, because many of the alleged victims and aggressors will no longer be subject to the military chain of command. Only an inquiry external to defence will be able to achieve that. And the investigation will need to reassure witnesses that they can comfortably give evidence without fear of retribution. This would be difficult under an internal defence investigation — a 2007 Defence Ombudsman’s report found that a significant proportion of defence force members surveyed did not feel comfortable making complaints.

But the outcome of a Royal Commission may be entirely disappointing: for the public, for defence, and for the alleged victims. For the victims, a Royal Commission may deliver neither convictions nor apologies. The facts will be murky and poorly documented. Some of the witnesses will be elderly. And the process may take years to reach any conclusions.

All the while there will be a daily media menu of depravity and disgust dressed in a military uniform. There will be little dignity for anyone in this process.

The damage to defence’s public image will be severe. It will compound a deepening sense of public malaise about the purpose and value of the defence force at a decisive moment in Australian strategic history. Our region has changed dramatically but our defence force has not. Much needed reform of defence capability, force structure, and organisation will be all the more difficult while the Royal Commission consumes ministerial oxygen.

The impact will be felt in defence recruitment, right at a time when defence leadership are focused on making defence a better career for women. What parent would encourage their child to join a defence force where s-xual predators allegedly roam the hallways of training schools?

Yet the irony is that most of the alleged s-xual predators will have long left defence and the current defence leadership have made eliminating such behaviour a priority. So the actions of a few will tarnish the reputations of thousands.

But the facts need to be established. Witnesses need to be called. And the question of how institutionalised criminal s-xual behaviour is in the ADF must be answered. A royal commission awaits, and the outcomes may be painful for all those involved.